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Comparison of practical techniques to develop latent fingermarks on fired and unfired cartridge cases
Forensic Science International 250 (2015) 17–26
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Comparison of practical techniques to develop latent fingermarks on fired and unfired cartridge cases Carlos M.A. Girelli a,b,*, Bernardo J.M. Lobo c, Alfredo G. Cunha a, Jair C.C. Freitas a, Francisco G. Emmerich a a b c
Laboratory of Carbon and Ceramic Materials, Department of Physics, Federal University of Espirito Santo, 29075-910 Vitoria, ES, Brazil Identification Group, Federal Police Department of Brazil, 29114-670 Vila Velha, ES, Brazil Identification Group, Federal Police Department of Brazil, 79904-644 Ponta Pora, MS, Brazil
A R T I C L E I N F O
A B S T R A C T
Article history: Received 29 November 2014 Received in revised form 11 February 2015 Accepted 12 February 2015 Available online 18 February 2015
We have tested some widely used and practical fingermark enhancement techniques such as powdering (regular powder dusting and magnetic powder application), cyanoacrylate fuming, fluorescent dying (basic yellow 40), gun blueing solutions and acidified hydrogen peroxide solutions. The results were evaluated and compared in order to establish best procedures on processing cartridge cases. The tests were performed on brass discs subjected to three different temperatures (room temperature, 63 and 200 8C), and on fired and unfired cartridge cases. All the samples were processed after three different periods of time (24 h, 7 days and 14 days) after deposition. The best results for both fired and unfired cartridge cases were obtained by the sequential application of cyanoacrylate, gun blueing solution and basic yellow 40. Some stages of the firing process were isolated in order to identify their effects over the final amount and quality of the remaining latent fingermarks on cartridge cases. Good state fingermarks were developed on unfired cartridge cases cycled through the gun, showing that friction inside the gun without firing does not cause significant damage to the fingermarks. On the other hand, fired cartridge cases are significantly affected by the firing effects, exhibiting low quality ridge details which are mainly located next to base. An unexpected phenomenon was observed on most of the brass discs heated to 200 8C and developed with gun blueing solutions; they presented a reverse development compared to the expected one, with darkening of the ridges instead of the background. ß 2015 Elsevier Ireland Ltd. All rights reserved.
Keywords: Fingermark Cartridge case Cyanoacrylate Gun blue Basic yellow 40 Reverse development
1. Introduction The fingermark recovery on fired cartridge cases is a challenge. There are discussions about the best methods to be used and a small proportion of cases with positive identification of suspects are reported [1–5]. Some important fingermark enhancement techniques are cyanoacrylate fuming (CA) [3–11], regular powder dusting (RP) and magnetic powder application (MP) [2,5,6,8,12], fluorescent dying [3,4,6–8,11] such as basic yellow 40 (BY40), gun blueing mixtures (GB) [6,7,9–11], acidified hydrogen peroxide (AHP) [8,9], vacuum metal deposition [6,13,14], palladium salts
* Corresponding author at: Identification Group, Federal Police Department of Brazil, Av. Vale do Rio Doce, 01, 29114-670 Vila Velha, Espirito Santo, Brazil. Tel.: +55 27 3041 8089; fax: +55 27 3041 8064. E-mail addresses: [email protected], [email protected] (Carlos M.A. Girelli). http://dx.doi.org/10.1016/j.forsciint.2015.02.012 0379-0738/ß 2015 Elsevier Ireland Ltd. All rights reserved.
[7,10], electrolysis [6,15,16], electrostatic deposition [1,10,17] and scanning Kelvin probe [18–20]. Some of these techniques and developers are expensive and require technical refinements that are not available for routine forensic applications, such as mentioned by Williams [19] for the use of scanning Kelvin probe. The use of CA as a primary enhancement technique is required for the application of some techniques such as fluorescent dying with BY40, and is recommended for others such as powdering and GB. The aim of this study was to gather and evaluate under the same conditions some widely used and available fingermark enhancement techniques to recovery latent fingermarks from fired and unfired cartridge cases. The results can be used in order to optimize procedures for latent fingermark experts when processing this kind of evidence. A number of experiments were performed on different substrates under various conditions, aiming at isolating some stages of the firing process to determine their influence on the quantity and quality of the remaining latent fingermarks in fired cartridge cases.
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2. Material and methods 2.1. Techniques and developers
A scanning electron microscope (SEM) was used to obtain more details about the effects of the development methods on the brass surfaces. SEM images were provided by a Shimadzu SSX-550 operating at low voltage (1–5 kV) by secondary electron imaging.
The development sequences used are referred to as: 2.2. Experiments on brass discs - CA + RP: cyanoacrylate followed by regular powder dusting; - CA + MP: cyanoacrylate followed by magnetic powder application; - CA + GB: cyanoacrylate followed by gun blue solution; - CA + BY40: cyanoacrylate followed by basic yellow 40 dying; - GB: gun blue solution; - AHP: acidified hydrogen peroxide, using glacial acetic acid (AHP1) or a household vinegar (AHP2). The CA fuming was performed on a fuming chamber with dimensions of 36, 56 and 31 cm, at room temperature and ambient pressure, using 20 drops of CA (Sirchie cat. N8 CNA103) for each set of 16 discs or 60 cartridge cases, during 30 min. To improve the polymerization, receptacles with hot water (temperature 80 8C, volume 200 ml, evaporating surface area 130 cm2) were placed inside the chamber during the fuming process, increasing the relative humidity to the range of 80–90%. These parameters were chosen based on preliminary tests and were used for all samples in this work (discs and cartridge cases). The relative humidity is a crucial factor for the effectiveness of the CA process [21] and should be controlled whenever possible to allow for better results. RP (Sirchie cat. N8 SB201L) and MP (Sirchie cat. N8 BPM114L) were applied using Marabou Feather Duster black (Sirchie cat. N8 123LB) and Magnetic Powder Applicator (Sirchie cat. N8 125L), respectively. The GB solutions were prepared using a 1:40 volume ratio of GB (Tetra Gun–Liquid Blue) in deionized water. This concentration is based on previous work [7,9–11] and allows a gradual and controllable development of fingermarks. After fully immersing each sample in the solution, the gradual development was monitored visually until a desired stage. The samples were then rinsed with deionized water, interrupting the development, and left to dry on paper towels. The developing time was typically between 5 and 10 min. The BY40 solution was obtained dissolving 2 g of basic yellow 40 (Sirchie cat. N8 LV507) in 1000 ml of methanol [10,22]. The samples were sprayed with the solution and, after a few seconds, rinsed with deionized water and left to dry on paper towel. The AHP1 solutions were obtained by diluting 5.2 ml of glacial acetic acid and 12.6 ml of a 35% hydrogen peroxide solution with deionized water giving a total volume of 250 ml [8,9]. The AHP2 solutions were prepared similarly to the AHP1 solution, but using 104 ml of household 5% vinegar instead of the glacial acetic acid. The samples submitted to this technique were fully immersed into the solution and gently stirred to release the little bubbles formed on the surface. After several seconds, they were removed and lightly rinsed with deionized water and left do dry on paper towels. A third AHP formulation [9], composed by household 5% vinegar and household 3% hydrogen peroxide at the volume ratio of 14.1:20 was tested aside to verify the possibility of employing this more homemade formulation. The latent fingermarks were photographed immediately before and after each development stage [11,23] using a Nikon D70s camera, equipped with macro lens and mounted on a forensic photographic table, applying direct and oblique illumination. To capture fluorescent latent fingermarks developed by BY40, a Lumatec Superlite 400 light source was used with blue light (460 nm) and an orange viewing filter.
Alpha brass discs 0.9 mm thick were cut by stamping to 50 mm diameter flat discs. Alpha phase brass is a low zinc content brass (30% Zn/70% Cu in weight) similar to that used in cartridge cases. The discs were washed with warm water (30–40 8C) containing 3–4 drops of a commercial detergent for each 500 ml of water, being vigorously rubbed by fabric for 30 s, followed by a rinse with deionized water and left to dry to the air, resting over paper towels [24]. Each disc received a natural fingermark from a donor that washed the hands with soap and waited 20 min before the deposition, without any artificial stimulus other than rubbing one hand against the other in order to homogenize the sweat distribution. Two individuals donated the fingermarks from their right thumbs and forefingers, generating groups with 4 discs. Each set of discs was exposed to a different temperature: room temperature (RT = 22 4 8C), 63 and 200 8C. The heating to attain the temperatures of 63 and 200 8C was performed on a hot plate within 1 h after the fingermarks deposition. The temperature measurements were performed with a K-type thermocouple in contact with the metallic surface where the fingermark was deposited. The heating times to reach the desired temperatures were about 10 s for 63 8C and 1 min for 200 8C. The samples were left to cool down naturally in ambient air. The 63 8C temperature was chosen because it is the maximum external temperature achieved by the surface of brass cartridge cases (cal. 9 mm) fired from regular pistol immediately after firing [25]. The 200 8C temperature was chosen to highlight the possible occurrence of some phenomena not clearly observed in the case of the samples heated up to 63 8C and it is also useful for comparison to results reported by other researchers [10,17,23,26,27]. The latent fingermarks developments using each one of the 7 techniques, for each temperature, was carried out after 3 time periods between the deposition of the fingermark and the developing process: 24 h, 7 days and 14 days. These time intervals can be considered reasonable when compared to real cases [23]. During these time intervals, the samples were subjected to the laboratory conditions (22 4 8C and 50 15% of relative humidity). The total number of discs processed was 252, which corresponds to the product of (4 discs/group) (3 temperatures) (7 techniques) (3 time intervals). The fingermarks developed on brass discs were evaluated by two independent experts following a 0 4 grading scale devised by Bandey [21,28]: 0—No ridge detail; 1—Less than 1/3 clear ridge detail; 2—Less than 2/3 clear ridge detail; 3—Incomplete (but > 2/3) clear ridge detail; 4—Complete clear ridge detail.
2.3. Experiments on unfired cartridge cases Unfired cartridge cases (live rounds) of brass (cal. 9 mm; manufactured by Companhia Brasileira de Cartuchos (CBC); model NTA) were separated as control samples. Natural fingermarks, obtained as described in Section 2.2, were carefully posted at the lateral surface of the cartridges. Then, they were developed by all techniques and after the same time intervals mentioned above (24 h, 7 and 14 days). Since they were new cartridges, no cleaning was performed before depositing the fingermarks; this was done to
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maintain conditions similar to the ones that ammunition might be found inside magazines and guns recovered from crime scenes. The objective of this phase was to verify if the techniques work well for unfired cartridge cases and to enable comparisons with the results obtained for unheated brass discs. The total number of samples at this phase was 21. 2.4. Experiments on unfired cartridge cases cycled through the gun One hundred unfired cartridge cases (live rounds) were prepared as in Section 2.3 with deposited fingermarks and then divided into 2 groups. Each group followed a path as described below: (a) Each cartridge was inserted directly in the barrel’s chamber of the gun (Glock 17), using gloves and tweezers, and the gun was closed pushing the slide stop. The cartridge was then ejected, by rapidly pulling back the slide, and collected from the floor for analysis; (b) The magazine was filled with cartridges and then inserted in the same gun used before in (a), the remaining steps of ejection and collection following the same procedure previously performed, including details like the position of the gun relative to the floor. The objective of this phase was to verify the mechanical effects caused to the latent fingermarks only by pure friction, without events involving high temperatures, high pressures or other effects of firing. The visualization of the latent fingermarks was obtained using the techniques that showed the best results obtained with the brass discs (Section 2.2) and with the control samples (Section 2.3). 2.5. Experiments on fired cartridge cases In order to apply the developing techniques tested before on discs, 500 live rounds (cal. 9 mm; manufacturer CBC; model NTA) were fired using two Glock 17 pistols. In order to reproduce actual firing conditions as close as possible, no special care was taken by the donors while manipulating the cartridges: no gloves were used; the hands were not washed; neither artificial eccrine or sebaceous stimulus was employed; the introduction of the cartridges into the magazines and of these into the guns were performed naturally; no long firing intervals were taken so as to avoid that the barrel could cool down; the guns were not cleaned at any moment. After ejection, the fired cartridges fell freely on the ground. They were carefully collected using gloves and plastic tweezers, and separated randomly in groups of 20 units. Each group was processed by one of the 7 techniques after one of the 3 time intervals of 24 h, 7 days and
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14 days. Thus, the total number of samples processed at this stage was 420 out of 500 fired cartridge cases. The fingermarks developed on fired cartridge cases were evaluated by two independent experts. The grading scale devised by Bandey [28] was slightly modified only in grade 1, aiming to refine the assessment of the effectiveness of the techniques and to take into account the great difference between the ridge details developed only on the base of the cartridges and the ridge details developed beyond the base of the cartridges. The grade 1 of Bandey’s grading scale was subdivided into 2 levels: 1A—Ridge detail close to the cartridge base (weight 0.5); 1B—Ridge detail beyond the cartridge base (weight 1.0).
3. Results 3.1. Latent fingermarks on brass discs In the case of the analyzed flat brass discs, the latent fingermarks could be seen without any developer application, just by using correct lighting. According to the 0–4 grading scale devised by Bandey [28], the average grade of the fingermarks before and after heating was 3.9. Fig. 1 shows the same fingermark photographed using oblique light before and after heating to 63 8C (1st day), and after CA fuming (14th day), exhibiting grade 4 in all stages. Following the work plan, all techniques were performed and classified according to their results, which are summarized in Table 1 and allow further comparisons with the results obtained from the cartridges. By way of illustration, Fig. 2 shows developments on brass discs from all tested techniques, under the same conditions (63 8C, 14 days), which are supposedly similar to real cases. The images in Fig. 2 are displayed in decreasing order of the average grade given in Table 1. Based on the results shown in Table 1, the classification of the techniques in descending order is: CA, CA + RP, CA + GB, CA + BY40, CA + MP, GB, AHP1, AHP2. Considering that the initial average grade of the fingermarks visualized with oblique illumination on the flat surface was 3.9, all techniques interfered with the marks nearly maintaining or decreasing the grading. Pure CA and CA + RP presented the best results, when illuminated by oblique light, causing negligible average grading changes. CA + GB, CA + BY40 and CA + MP also presented good results using, respectively, natural, UV and oblique lighting. GB without CA presented medium results with natural lighting. The two tested AHP formulas did not present good results on the discs compared with the other techniques; they tended to blur the surfaces and only in few cases identifiable fingermarks were retrieved.
Fig. 1. Typical grade-4 fingermark on brass disc photographed using oblique lighting: (a) 1st day, within 1 h after deposition; (b) 1st day, after heating to 63 8C; (c) 14th day, after CA fuming.
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Table 1 Evaluation of fingermarks developed on brass discs following the 0–4 grading scale devised by Bandey [28]. Technique
Room temperature
63 8C
Average gradea
CA CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2 a b c
Average RTb
24 h
7 days
14 days
3.8 3.4 2.4 3.4 3.6 2.4 0.0 0.0
3.9 3.9 3.7 4.0 4.0 2.1 1.3 1.3
3.8 3.6 2.9 3.0 2.5 2.1 2.4 1.4
3.8 3.6 3.0 3.4 3.4 2.2 1.2 0.9
200 8C
Average gradea
Average 63 8Cb
24 h
7 days
14 days
3.8 3.6 2.9 2.6 2.9 2.5 0.5 1.1
3.9 3.8 3.4 3.9 3.9 2.6 1.5 1.4
4.0 3.9 3.4 3.4 3.8 3.1 0.8 0.6
3.9 3.8 3.2 3.3 3.5 2.8 0.9 1.0
Final gradec
Average gradea
Average 200 8Cb
24 h
7 days
14 days
3.7 4.0 3.6 3.5 3.3 3.8 1.4 0.6
4.0 4.0 4.0 4.0 4.0 1.4 1.4 1.4
3.7 3.6 3.6 2.6 3.0 2.4 0.5 1.1
3.8 3.9 3.8 3.4 3.4 2.5 1.1 1.0
3.8 3.8 3.3 3.4 3.4 2.5 1.1 1.0
Average grade is obtained by the evaluation of 4 fingermarks by two independent experts. Each value corresponds to the average obtained over the three periods of time (24 h, 7 days, 14 days) for each temperature. Final grade of the technique is the average over the three periods of time and over the three temperatures (RT, 63 8, 200 8C).
GB and CA + GB generated good contrast, but in many cases showed the inconvenience of reacting irregularly, causing incomplete or partially overdeveloped areas. Fig. 3 shows a typical case of non-uniform development by GB. A possible procedure to avoid this issue is to photograph the sample periodically during the development, recording new sections without losing the earliest ones by the overdeveloping. The final image can be constructed by overlapping successive pictures, using basic computational tools available in commercial image editing software. An unexpected phenomenon was observed in the case of GB (and CA + GB) developments on most of the discs heated to 200 8C.
In regular developments, the GB solutions react with the metallic surface making it darker while the regions protected by the fingermark ridge residues remain clear [9,22] (see Fig. 4 for disc heated to 63 8C). However, in many of the discs heated up to 200 8C the opposite effect occurred: a reverse development characterized by dark ridges and bright background. Fig. 5 shows a reverse development by GB on a disc preheated up to 200 8C. SEM images of regular and reverse developments using GB are shown in Figs. 6 and 7, respectively. In Fig. 6 the regular corrosion of the non-protected regions (valleys) is obvious, whereas in Fig. 7 the action of GB is predominantly along the ridges.
Fig. 2. Fingermarks developed on brass discs by the tested techniques (63 8C, 14 days).
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Fig. 3. Partial development by GB on a brass disc (63 8C, 24 h).
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Fig. 6. SEM image of regular GB development on brass disc.
Fig. 4. Regular development by GB on brass disc preheated up to 63 8C.
Fig. 7. SEM image of reverse GB development on brass disc.
3.2. Latent fingermarks on unfired cartridge cases
Fig. 5. Reverse development by GB on brass disc preheated up to 200 8C.
Some temperature effects on brass that can explain this phenomenon involve oxide films growth and pitting corrosion [17,26,27]. The existence of a pattern in this behavior could give rise to a new methodology of developing fingermarks on metallic surfaces subjected to heating. In addition to the suspect identification, the technique could provide relevant information, for example, on the question if the developed fingermark was deposited before or after an eventual heating of the surface.
Developments on unfired cartridge cases (control samples) are shown in Fig. 8. Different from the flat brass discs, it was not possible to visualize latent fingermarks on cartridge cases without the application of some enhancement technique. The visualization of fingermarks in cartridge cases only by the application of oblique light from common flashlights is more complicated due to the cylindrical shape and the surface conditions of the cartridge cases. CA + RP and CA + MP presented good results for relatively fresh fingermarks (24 h and 7 days), but not so for aged fingermarks (14 d). All the other techniques developed relatively good fingermarks for the 3 elapsed times (24 h, 7 days and 14 days), including AHP1 and AHP2, which did not work well with brass discs. 3.3. Latent fingermarks on unfired cartridge cases cycled through the gun Based on the results obtained from the previous phases, the CA + GB + BY40 sequence was used to develop fingermarks on the unfired cartridge cases. The first technique applied was CA, which produced very good results for discs and unfired cartridge cases (control samples). RP could be applied after CA, since it has also produced good results and because it seems to be compatible with
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Fig. 8. Developments by all tested techniques on unfired cartridge cases (control samples) for all elapsed times (24 h, 7 days and 14 days).
the subsequent application of GB and BY40. However, as the RP results were not better than those by CA under the same lighting conditions, this step was neglected. The sequence of better graduated techniques is CA + GB, which marks the surface and thus allows the visualization of fingermarks without the need of oblique lighting. The next technique in the ranking is CA + BY40, which requires UV light to generate fluorescence of the fingermarks. The combination of these 3 compatible techniques, using
3 different lighting sources, enlarges the possibility of obtaining good results. Fig. 9 shows the cartridges that were placed directly in the barrel’s chamber and then were ejected. This process did little damage to the latent fingermarks. The latent marks in cartridges submitted to the longer cycle (involving the loading of the magazine) were more damaged than those from cartridges inserted directly in the chamber, as can be
Fig. 9. Developments by 3 successive techniques (CA + GB + BY40) on 3 different samples inserted directly into the barrel’s chamber and then ejected.
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Fig. 10. Developments by 3 successive techniques on different samples that followed the whole cycle of loading the gun and then were ejected.
seen in Fig. 10. The crushing and the overlapping of the impressions are clearly visible. Nevertheless, enough areas for identification were recovered, indicating that processes involving only friction, without firing, are not the major responsible for the high degradation of the latent fingermarks on fired cartridge cases. 3.4. Latent fingermarks on fired cartridge cases In the case of fired cartridge cases naturally handled prior to firing, sets of 20 cartridges were developed by each technique for each period of elapsed time after firing. No fingermark with Bandey’s grade equal or superior to 2 was developed on fired cartridge cases. The statistics with the average number of fired cartridge cases with grades 0, 1A and 1B is displayed in Table 2. Based on the statistics from Table 2, and considering the weights 0, 0.5 and 1.0, respectively, for grades 0, 1A and 1B, the average grades for fingermarks developed on fired cartridge cases using each technique were evaluated and are displayed in Table 3. The low values of the observed average grades indicate the significant difficulty associated with the recoverability of fingermarks from fired cartridge cases. The techniques that presented the best results involved CA, BY40 and GB, which is in agreement with refs. [6,7]. As CA protects the latent fingermarks, it is strongly recommended to make use of it before any other technique. Furthermore, the possibility of the cumulative use of CA, GB and BY40 increases the chances of obtaining good developments. Fig. 11 shows the application of this sequence to a single grade-1B fired cartridge case. Some of the best developments obtained in this phase are shown in Fig. 12. They were developed using the sequence CA + GB + BY40 and all of them presented grade 1B. The homemade formulation of AHP using household vinegar and household hydrogen peroxide presented
similar results (not shown) to those obtained from AHP1 and AHP2 formulations. As shown in Fig. 13, most of the ridge details developed were found close to the cartridge base (grade 1A). This is in accord with the results of Williams [20] and Bhaloo et al. [10]. Furthermore, a narrow zone that extends from the base to near the opening of the cartridge case can be observed in many samples, as shown in Figs. 14 and 15. This pattern was also observed by Bhaloo et al. [10]. According to those authors, this narrow zone corresponds to the surface of the cartridge case adjacent to the top of the barrel of the firearm, which does not show as much evidence of damage as its opposite side adjacent to the bottom-most part of the chamber of the firearm.
Table 3 Evaluation of average grades of the fingermarks developed on fired cartridge cases following the slightly modified Bandey’s grading scale (cf. Section 2.5). Technique
CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2
Average gradea
Total average gradeb
24 h
7 days
14 days
0.04 0.05 0.39 0.29 0.15 0.08 0.06
0.05 0.10 0.28 0.18 0.19 0.04 0.08
0.05 0.03 0.21 0.09 0.13 0.04 0.06
0.05 0.06 0.29 0.18 0.15 0.05 0.07
a Average grade obtained by two independent examiners for sets of 20 fired cartridge cases. b Total average grade obtained over the three periods of time (24 h, 7 days, 14 days).
Table 2 Statistics with the average number of fired cartridge cases (for sets of 20 samples) with grades 0, 1A and 1B evaluated by two independent experts following the slightly modified Bandey’s grading scale (cf. Section 2.5) for each period of elapsed time after firing. Technique
24 h 0
1A
1B
0
1A
1B
0
1A
1B
CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2
18.5 18.0 9.5 11.0 15.5 17.5 17.5
1.5 2.0 5.5 6.5 3.0 2.0 2.5
0.0 0.0 5.0 2.5 1.5 0.5 0.0
18.0 17.0 12.0 15.0 14.5 18.5 17.5
2.0 2.0 5.0 3.0 3.5 1.5 2.0
0.0 1.0 3.0 2.0 2.0 0.0 0.5
18.5 19.0 14.0 17.5 16.0 18.5 18.0
1.0 1.0 3.5 1.5 3.0 1.5 1.5
0.5 0.0 2.5 1.0 1.0 0.0 0.5
7 days
14 days
Fig. 11. Application of the sequence CA + GB + BY40 to a single fired cartridge case.
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Fig. 12. Some of the best developments on fired cartridge cases of different ages naturally handled before firing. They were developed using the sequence CA + GB + BY40 and all of them were graded as 1B.
Fig. 13. Grade 1A typical developments indicating the base of the fired cartridge cases as the richest minutiae area.
Fig. 14. CA development pattern seen in 3608 showing a narrow zone that extends from the base to near the opening of the case.
4. Discussion The visualization of fingermarks on planar metallic surfaces without the application of developers, only using oblique lighting, can be explained by optical interference of the light [29]. This resource was successfully used to visualize fingermarks on flat brass discs, but did not work so well for brass cartridge cases using common flashlights, probably because of the cylindrical shape and surface conditions of the cartridge cases.
The performed experiments demonstrated that heated brass discs do not accurately reproduce the effects of real firing over latent fingermarks on fired cartridges surfaces. The heat treatments of the discs described in Section 2.2 (simulating the real maximum temperatures achieved by the external surfaces of fired cartridges) did not prevent the visualization of the latent fingermarks, in agreement with previous reports by Migron et al. [30], and Wiesner and Springer [31].
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Fig. 15. GB development pattern seen in 3608 showing a narrow zone that extends from the base to near the opening of the case.
Likewise, the frictions experimented by the unfired cartridges going through the gun parts (without firing) did not cause significant damage to the latent fingermarks as the global effects generated by firing, corroborating the conclusions of Wiesner and Springer [31]. Therefore, other factors besides temperature and pure friction act over the cartridges during firing, causing the effects observed in Section 3.4. Three possible factors can be responsible for the damages caused to the latent fingermarks on fired cartridges [6,12,31]: (1) The blowback of the hot gases produced by the propellant burning, which wipes great part of the lateral surface of the cartridge, once the barrel’s chamber is not perfectly sealed and may leave some looseness between the cartridge and the chamber; (2) The expansion of the cartridge due to the elevated internal pressure, which maximizes the friction between the lateral surface of the cartridge and the chamber during the ejection. As the thickness of the cartridge wall is smaller next to the opening and reinforced next to the base, this last region tends to suffer less expansion, justifying the predominance of ridge details found closer to the cartridge base. (3) The influence of the propellant byproducts brought by the blowback of gases, generating coatings that may affect development and visualization of latent fingermarks. These factors cause noticeable differences between the simulations without firing and the tests with firing and may depend on the gun and ammunition characteristics, such as caliber, type and geometry of the chamber, amount and composition of the propellant [6,10]. In addition to these factors related to the firing process, it is also possible that brass discs might be different in both chemical composition and surface condition from commercially manufactured cartridge cases. This could explain, for example, the discrepancy between the poor results for AHP developments on unheated brass discs (Table 1) and the good results obtained for unfired cartridge cases using the same techniques (Fig. 8). The reverse development by GB seen in brass discs heated up to 200 8C was not observed in fired cartridges. It can be thought as further evidence that the external surfaces of the fired cartridge cases do not reach temperatures as high as 200 8C, in according with conclusions of Gashi et al. [25].
5. Conclusions Among the tested techniques, those that showed the best consistency considering the results for both fired and unfired cartridge cases were CA, GB and BY40. The compatibility between them, which use different lighting sources, allows a combined use, increasing the possibility of obtaining better results. The suggested sequence is CA + GB + BY40, for both fired and unfired cartridge cases. The isolation of the loading and ejection processes indicated that friction inside the gun without firing does not cause significant damage to the fingermarks. Good state fingermarks were developed on unfired cartridge cases cycled through the gun. The firing effects over the fired cartridge cases resulted in significant loss of ridge details. The richest minutiae area was generally located next to the base. The patterns observed on the latent fingermarks recovered from fired cartridge cases indicate that the success in developing this kind of evidence depends not only on the techniques employed, but on a sum of factors. It is necessary that good fingermarks are produced, neither damaged nor overlapped during insertion in the magazine. These latent marks must be localized at the small regions that will survive from firing and ejection, and should present enough minutiae to allow comparison and individualization. Acknowledgements The authors would like to thank the National Institute of Identification of the Federal Police Department of Brazil (INI/ DIREX/DPF), in special the fingermark experts Eulemar Amorim and Luciene Marques for valuable help during the work. We also thank the Brazilian Association of the Federal Police Fingermark Experts (ABRAPOL) and the Brazilian agencies CAPES, CNPq, FAPES and FINEP for the partial financial support. References [1] J.W. Bond, D. Phil, B.A. Chuck Heidel, Visualization of latent fingerprint corrosion on a discharged brass shell casing, J. Forensic Sci. 54 (4) (2009) 892–894. [2] H.N. Freeman, Magnetic fingerprint powder on firearms and metal cartridges, J. Forensic Ident. 49 (5) (1999) 479–484. [3] S. Johnson, Development of latent prints on firearms evidence, J. Forensic Ident. 60 (2) (2010) 148–151. [4] A. Pratt, Fingerprints and firearms, J. Forensic Ident. 62 (3) (2012) 234–242. [5] B. Maldonado, Study on developing latent fingerprints on firearm evidence, J. Forensic Ident. 62 (5) (2012) 425–429. [6] R.K. Bentsen, J.K. Brown, A. Dinsmore, K.K. Harvey, T.G. Kee, Post firing visualisation of fingerprints on spent cartridge cases, Sci. Just. 36 (1) (1996) 3–8.
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[7] A.J. Dominick, K. Laing, A comparison of six fingerprint enhancement techniques for the recovery of latent fingerprints from unfired cartridge cases, J. Forensic Ident. 61 (2) (2011) 155–165. [8] K.E. Edmiston, J. Johnson, Determining an optimal sequence for chemical development of latent prints on cartridge casings and shotgun shells, J. Forensic Sci. 54 (6) 1327–1331. [9] A.A. Cantu, D.A. Leben, R. Ramotowski, J. Kopera, J.R. Simms, Use of acidified hydrogen peroxide to remove excess gun blue from gun blue-treated cartridge cases and to develop latent prints on untreated cartridge cases, J. Forensic Sci. 43 (2) (1998) 294–298. [10] Z.M. Bhaloo, B. Yamashita, D. Wilkinson, N.N. Dae´id, The recovery of fingerprints from fired cartridge cases: a comparison of current methods of development with an electrostatic deposition technique, Ident. Can. 33 (3) (2010) 88–102. [11] D.A. Leben, R.S. Ramotowski, Evaluation of Gun Blueing Solutions and Their Ability to Develop Fingerprints on Cartridge Casings, International Association for Identification Cheasapeake Division, FDIAI News, 1997, pp. 9–10. [12] B.W. Given, Latent fingerprints on cartridges and expended cartridge casings, J. Forensic Sci. 21 (3) (1976) 587–594. [13] A.S. Ramos, M.T. Vieira, An efficient strategy to detect latent fingermarks on metallic surfaces, Forensic Sci. Int. 217 (2012) 196–203. [14] G.L. Thomas, T.E. Reynoldson, Some observations on fingerprint deposits, J. Phys. D: Appl. Phys. 8 (1975) 724–729. [15] F. Nizam, W. Knaap, J.D. Stewart, Development of fingerprints using electrolysis: a technical report into the development of fingerprints on fired brass cartridge cases, J. Forensic Ident. 62 (2) (2012) 129–142. [16] O.P. Jasuja, G. Singh, J. Almog, Development of latent fingermarks by aqueous electrolytes, Forensic Sci. Int. 207 (2011) 215–222. [17] J.W. Bond, D. Phil, Visualization of latent fingerprint corrosion of metallic surfaces, J. Forensic Sci. 53 (4) (2008) 812–822. [18] G. Williams, H.N. McMurray, D.A. Worsley, Latent fingerprint detection using a scanning Kelvin microprobe, J. Forensic Sci. 46 (5) (2001) 1085–1092. [19] G. Williams, N. McMurray, Latent fingermark visualisation using a scanning Kelvin probe, Forensic Sci. Int. 167 (2007) 102–109.
[20] G. Williams, Visualisation of fingerprints on metal surfaces using a scanning Kelvin probe, Fingerprint Whorld 36 (2010) 51–60. [21] M. Paine, H.L. Bandey, S.M. Bleay, H. Willson, The effect of relative humidity on the effectiveness of the cyanoacrylate fuming process for fingermark development and on the microstructure of the developed marks, Forensic Sci. Int. 212 (2011) 130–142. [22] H.C. Lee, R.E. Gaensslen, Advances in Fingerprint Technology, third ed., CRC Press, Boca Raton, 2013. [23] T. Kent, Standardizing protocols for fingerprint reagent testing, J. Forensic Ident. 60 (3) (2010) 371–379. [24] E. Paterson, J.W. Bond, D. Phil, A.R. Hillman, A comparison of cleaning regimes for the effective removal of fingerprints deposits from brass, J. Forensic Sci. 55 (1) (2010) 221–224. [25] B. Gashi, M.R. Edwards, P.A. Sermon, L. Courtnei, D. Harrison, Y. Xu, Measurment of 9 mm cartridge case external temperatures and its forensic application, Forensic Sci. Int. 200 (2010) 21–27. [26] J.W. Bond, D. Phil, Optical enhancement of fingerprint deposits on brass using digital color mapping, J. Forensic Sci. 56 (5) (2011) 1285–1288. [27] G. Wightman, D. O’Connor, The thermal visualisation of latent fingermarks on metallic surfaces, Forensic Sci. Int. 204 (2011) 88–96. [28] H.L. Bandey, The powders process, Study 1: Evaluation of fingerprint brushes for use with aluminum powder, HOSDB Fingerprint Dev. Imaging Newslett.: Special Ed. 54 (4) (2004) 1–12. [29] J.W. Bond, T. Loe, Digital mapping of differential oxidation arising from fingerprint sweat deposits on a-phase brass, J. Assoc. Crime Scene Reconstruct. 17 (2) (2011) 19–24. [30] Y. Migron, G. Hocherman, E. Springer, J. Almog, D. Mandler, Visualization of sebaceous fingerprints on fired cartridge cases: a laboratory study, J. Forensic Sci. 43 (3) (1998) 543–548. [31] S. Wiesner, E. Springer, U. Argaman, A closer look at the effects of the shooting process on fingerprint development on fired cartridge cases, in: Proceedings of the International Symposium on Fingerprint Detection and Identification, June 26–30, 1995, Neurim, Israel, pp. 161–178.
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Forensic Science International journal homepage: www.elsevier.com/locate/forsciint
Comparison of practical techniques to develop latent fingermarks on fired and unfired cartridge cases Carlos M.A. Girelli a,b,*, Bernardo J.M. Lobo c, Alfredo G. Cunha a, Jair C.C. Freitas a, Francisco G. Emmerich a a b c
Laboratory of Carbon and Ceramic Materials, Department of Physics, Federal University of Espirito Santo, 29075-910 Vitoria, ES, Brazil Identification Group, Federal Police Department of Brazil, 29114-670 Vila Velha, ES, Brazil Identification Group, Federal Police Department of Brazil, 79904-644 Ponta Pora, MS, Brazil
A R T I C L E I N F O
A B S T R A C T
Article history: Received 29 November 2014 Received in revised form 11 February 2015 Accepted 12 February 2015 Available online 18 February 2015
We have tested some widely used and practical fingermark enhancement techniques such as powdering (regular powder dusting and magnetic powder application), cyanoacrylate fuming, fluorescent dying (basic yellow 40), gun blueing solutions and acidified hydrogen peroxide solutions. The results were evaluated and compared in order to establish best procedures on processing cartridge cases. The tests were performed on brass discs subjected to three different temperatures (room temperature, 63 and 200 8C), and on fired and unfired cartridge cases. All the samples were processed after three different periods of time (24 h, 7 days and 14 days) after deposition. The best results for both fired and unfired cartridge cases were obtained by the sequential application of cyanoacrylate, gun blueing solution and basic yellow 40. Some stages of the firing process were isolated in order to identify their effects over the final amount and quality of the remaining latent fingermarks on cartridge cases. Good state fingermarks were developed on unfired cartridge cases cycled through the gun, showing that friction inside the gun without firing does not cause significant damage to the fingermarks. On the other hand, fired cartridge cases are significantly affected by the firing effects, exhibiting low quality ridge details which are mainly located next to base. An unexpected phenomenon was observed on most of the brass discs heated to 200 8C and developed with gun blueing solutions; they presented a reverse development compared to the expected one, with darkening of the ridges instead of the background. ß 2015 Elsevier Ireland Ltd. All rights reserved.
Keywords: Fingermark Cartridge case Cyanoacrylate Gun blue Basic yellow 40 Reverse development
1. Introduction The fingermark recovery on fired cartridge cases is a challenge. There are discussions about the best methods to be used and a small proportion of cases with positive identification of suspects are reported [1–5]. Some important fingermark enhancement techniques are cyanoacrylate fuming (CA) [3–11], regular powder dusting (RP) and magnetic powder application (MP) [2,5,6,8,12], fluorescent dying [3,4,6–8,11] such as basic yellow 40 (BY40), gun blueing mixtures (GB) [6,7,9–11], acidified hydrogen peroxide (AHP) [8,9], vacuum metal deposition [6,13,14], palladium salts
* Corresponding author at: Identification Group, Federal Police Department of Brazil, Av. Vale do Rio Doce, 01, 29114-670 Vila Velha, Espirito Santo, Brazil. Tel.: +55 27 3041 8089; fax: +55 27 3041 8064. E-mail addresses: [email protected], [email protected] (Carlos M.A. Girelli). http://dx.doi.org/10.1016/j.forsciint.2015.02.012 0379-0738/ß 2015 Elsevier Ireland Ltd. All rights reserved.
[7,10], electrolysis [6,15,16], electrostatic deposition [1,10,17] and scanning Kelvin probe [18–20]. Some of these techniques and developers are expensive and require technical refinements that are not available for routine forensic applications, such as mentioned by Williams [19] for the use of scanning Kelvin probe. The use of CA as a primary enhancement technique is required for the application of some techniques such as fluorescent dying with BY40, and is recommended for others such as powdering and GB. The aim of this study was to gather and evaluate under the same conditions some widely used and available fingermark enhancement techniques to recovery latent fingermarks from fired and unfired cartridge cases. The results can be used in order to optimize procedures for latent fingermark experts when processing this kind of evidence. A number of experiments were performed on different substrates under various conditions, aiming at isolating some stages of the firing process to determine their influence on the quantity and quality of the remaining latent fingermarks in fired cartridge cases.
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2. Material and methods 2.1. Techniques and developers
A scanning electron microscope (SEM) was used to obtain more details about the effects of the development methods on the brass surfaces. SEM images were provided by a Shimadzu SSX-550 operating at low voltage (1–5 kV) by secondary electron imaging.
The development sequences used are referred to as: 2.2. Experiments on brass discs - CA + RP: cyanoacrylate followed by regular powder dusting; - CA + MP: cyanoacrylate followed by magnetic powder application; - CA + GB: cyanoacrylate followed by gun blue solution; - CA + BY40: cyanoacrylate followed by basic yellow 40 dying; - GB: gun blue solution; - AHP: acidified hydrogen peroxide, using glacial acetic acid (AHP1) or a household vinegar (AHP2). The CA fuming was performed on a fuming chamber with dimensions of 36, 56 and 31 cm, at room temperature and ambient pressure, using 20 drops of CA (Sirchie cat. N8 CNA103) for each set of 16 discs or 60 cartridge cases, during 30 min. To improve the polymerization, receptacles with hot water (temperature 80 8C, volume 200 ml, evaporating surface area 130 cm2) were placed inside the chamber during the fuming process, increasing the relative humidity to the range of 80–90%. These parameters were chosen based on preliminary tests and were used for all samples in this work (discs and cartridge cases). The relative humidity is a crucial factor for the effectiveness of the CA process [21] and should be controlled whenever possible to allow for better results. RP (Sirchie cat. N8 SB201L) and MP (Sirchie cat. N8 BPM114L) were applied using Marabou Feather Duster black (Sirchie cat. N8 123LB) and Magnetic Powder Applicator (Sirchie cat. N8 125L), respectively. The GB solutions were prepared using a 1:40 volume ratio of GB (Tetra Gun–Liquid Blue) in deionized water. This concentration is based on previous work [7,9–11] and allows a gradual and controllable development of fingermarks. After fully immersing each sample in the solution, the gradual development was monitored visually until a desired stage. The samples were then rinsed with deionized water, interrupting the development, and left to dry on paper towels. The developing time was typically between 5 and 10 min. The BY40 solution was obtained dissolving 2 g of basic yellow 40 (Sirchie cat. N8 LV507) in 1000 ml of methanol [10,22]. The samples were sprayed with the solution and, after a few seconds, rinsed with deionized water and left to dry on paper towel. The AHP1 solutions were obtained by diluting 5.2 ml of glacial acetic acid and 12.6 ml of a 35% hydrogen peroxide solution with deionized water giving a total volume of 250 ml [8,9]. The AHP2 solutions were prepared similarly to the AHP1 solution, but using 104 ml of household 5% vinegar instead of the glacial acetic acid. The samples submitted to this technique were fully immersed into the solution and gently stirred to release the little bubbles formed on the surface. After several seconds, they were removed and lightly rinsed with deionized water and left do dry on paper towels. A third AHP formulation [9], composed by household 5% vinegar and household 3% hydrogen peroxide at the volume ratio of 14.1:20 was tested aside to verify the possibility of employing this more homemade formulation. The latent fingermarks were photographed immediately before and after each development stage [11,23] using a Nikon D70s camera, equipped with macro lens and mounted on a forensic photographic table, applying direct and oblique illumination. To capture fluorescent latent fingermarks developed by BY40, a Lumatec Superlite 400 light source was used with blue light (460 nm) and an orange viewing filter.
Alpha brass discs 0.9 mm thick were cut by stamping to 50 mm diameter flat discs. Alpha phase brass is a low zinc content brass (30% Zn/70% Cu in weight) similar to that used in cartridge cases. The discs were washed with warm water (30–40 8C) containing 3–4 drops of a commercial detergent for each 500 ml of water, being vigorously rubbed by fabric for 30 s, followed by a rinse with deionized water and left to dry to the air, resting over paper towels [24]. Each disc received a natural fingermark from a donor that washed the hands with soap and waited 20 min before the deposition, without any artificial stimulus other than rubbing one hand against the other in order to homogenize the sweat distribution. Two individuals donated the fingermarks from their right thumbs and forefingers, generating groups with 4 discs. Each set of discs was exposed to a different temperature: room temperature (RT = 22 4 8C), 63 and 200 8C. The heating to attain the temperatures of 63 and 200 8C was performed on a hot plate within 1 h after the fingermarks deposition. The temperature measurements were performed with a K-type thermocouple in contact with the metallic surface where the fingermark was deposited. The heating times to reach the desired temperatures were about 10 s for 63 8C and 1 min for 200 8C. The samples were left to cool down naturally in ambient air. The 63 8C temperature was chosen because it is the maximum external temperature achieved by the surface of brass cartridge cases (cal. 9 mm) fired from regular pistol immediately after firing [25]. The 200 8C temperature was chosen to highlight the possible occurrence of some phenomena not clearly observed in the case of the samples heated up to 63 8C and it is also useful for comparison to results reported by other researchers [10,17,23,26,27]. The latent fingermarks developments using each one of the 7 techniques, for each temperature, was carried out after 3 time periods between the deposition of the fingermark and the developing process: 24 h, 7 days and 14 days. These time intervals can be considered reasonable when compared to real cases [23]. During these time intervals, the samples were subjected to the laboratory conditions (22 4 8C and 50 15% of relative humidity). The total number of discs processed was 252, which corresponds to the product of (4 discs/group) (3 temperatures) (7 techniques) (3 time intervals). The fingermarks developed on brass discs were evaluated by two independent experts following a 0 4 grading scale devised by Bandey [21,28]: 0—No ridge detail; 1—Less than 1/3 clear ridge detail; 2—Less than 2/3 clear ridge detail; 3—Incomplete (but > 2/3) clear ridge detail; 4—Complete clear ridge detail.
2.3. Experiments on unfired cartridge cases Unfired cartridge cases (live rounds) of brass (cal. 9 mm; manufactured by Companhia Brasileira de Cartuchos (CBC); model NTA) were separated as control samples. Natural fingermarks, obtained as described in Section 2.2, were carefully posted at the lateral surface of the cartridges. Then, they were developed by all techniques and after the same time intervals mentioned above (24 h, 7 and 14 days). Since they were new cartridges, no cleaning was performed before depositing the fingermarks; this was done to
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maintain conditions similar to the ones that ammunition might be found inside magazines and guns recovered from crime scenes. The objective of this phase was to verify if the techniques work well for unfired cartridge cases and to enable comparisons with the results obtained for unheated brass discs. The total number of samples at this phase was 21. 2.4. Experiments on unfired cartridge cases cycled through the gun One hundred unfired cartridge cases (live rounds) were prepared as in Section 2.3 with deposited fingermarks and then divided into 2 groups. Each group followed a path as described below: (a) Each cartridge was inserted directly in the barrel’s chamber of the gun (Glock 17), using gloves and tweezers, and the gun was closed pushing the slide stop. The cartridge was then ejected, by rapidly pulling back the slide, and collected from the floor for analysis; (b) The magazine was filled with cartridges and then inserted in the same gun used before in (a), the remaining steps of ejection and collection following the same procedure previously performed, including details like the position of the gun relative to the floor. The objective of this phase was to verify the mechanical effects caused to the latent fingermarks only by pure friction, without events involving high temperatures, high pressures or other effects of firing. The visualization of the latent fingermarks was obtained using the techniques that showed the best results obtained with the brass discs (Section 2.2) and with the control samples (Section 2.3). 2.5. Experiments on fired cartridge cases In order to apply the developing techniques tested before on discs, 500 live rounds (cal. 9 mm; manufacturer CBC; model NTA) were fired using two Glock 17 pistols. In order to reproduce actual firing conditions as close as possible, no special care was taken by the donors while manipulating the cartridges: no gloves were used; the hands were not washed; neither artificial eccrine or sebaceous stimulus was employed; the introduction of the cartridges into the magazines and of these into the guns were performed naturally; no long firing intervals were taken so as to avoid that the barrel could cool down; the guns were not cleaned at any moment. After ejection, the fired cartridges fell freely on the ground. They were carefully collected using gloves and plastic tweezers, and separated randomly in groups of 20 units. Each group was processed by one of the 7 techniques after one of the 3 time intervals of 24 h, 7 days and
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14 days. Thus, the total number of samples processed at this stage was 420 out of 500 fired cartridge cases. The fingermarks developed on fired cartridge cases were evaluated by two independent experts. The grading scale devised by Bandey [28] was slightly modified only in grade 1, aiming to refine the assessment of the effectiveness of the techniques and to take into account the great difference between the ridge details developed only on the base of the cartridges and the ridge details developed beyond the base of the cartridges. The grade 1 of Bandey’s grading scale was subdivided into 2 levels: 1A—Ridge detail close to the cartridge base (weight 0.5); 1B—Ridge detail beyond the cartridge base (weight 1.0).
3. Results 3.1. Latent fingermarks on brass discs In the case of the analyzed flat brass discs, the latent fingermarks could be seen without any developer application, just by using correct lighting. According to the 0–4 grading scale devised by Bandey [28], the average grade of the fingermarks before and after heating was 3.9. Fig. 1 shows the same fingermark photographed using oblique light before and after heating to 63 8C (1st day), and after CA fuming (14th day), exhibiting grade 4 in all stages. Following the work plan, all techniques were performed and classified according to their results, which are summarized in Table 1 and allow further comparisons with the results obtained from the cartridges. By way of illustration, Fig. 2 shows developments on brass discs from all tested techniques, under the same conditions (63 8C, 14 days), which are supposedly similar to real cases. The images in Fig. 2 are displayed in decreasing order of the average grade given in Table 1. Based on the results shown in Table 1, the classification of the techniques in descending order is: CA, CA + RP, CA + GB, CA + BY40, CA + MP, GB, AHP1, AHP2. Considering that the initial average grade of the fingermarks visualized with oblique illumination on the flat surface was 3.9, all techniques interfered with the marks nearly maintaining or decreasing the grading. Pure CA and CA + RP presented the best results, when illuminated by oblique light, causing negligible average grading changes. CA + GB, CA + BY40 and CA + MP also presented good results using, respectively, natural, UV and oblique lighting. GB without CA presented medium results with natural lighting. The two tested AHP formulas did not present good results on the discs compared with the other techniques; they tended to blur the surfaces and only in few cases identifiable fingermarks were retrieved.
Fig. 1. Typical grade-4 fingermark on brass disc photographed using oblique lighting: (a) 1st day, within 1 h after deposition; (b) 1st day, after heating to 63 8C; (c) 14th day, after CA fuming.
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Table 1 Evaluation of fingermarks developed on brass discs following the 0–4 grading scale devised by Bandey [28]. Technique
Room temperature
63 8C
Average gradea
CA CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2 a b c
Average RTb
24 h
7 days
14 days
3.8 3.4 2.4 3.4 3.6 2.4 0.0 0.0
3.9 3.9 3.7 4.0 4.0 2.1 1.3 1.3
3.8 3.6 2.9 3.0 2.5 2.1 2.4 1.4
3.8 3.6 3.0 3.4 3.4 2.2 1.2 0.9
200 8C
Average gradea
Average 63 8Cb
24 h
7 days
14 days
3.8 3.6 2.9 2.6 2.9 2.5 0.5 1.1
3.9 3.8 3.4 3.9 3.9 2.6 1.5 1.4
4.0 3.9 3.4 3.4 3.8 3.1 0.8 0.6
3.9 3.8 3.2 3.3 3.5 2.8 0.9 1.0
Final gradec
Average gradea
Average 200 8Cb
24 h
7 days
14 days
3.7 4.0 3.6 3.5 3.3 3.8 1.4 0.6
4.0 4.0 4.0 4.0 4.0 1.4 1.4 1.4
3.7 3.6 3.6 2.6 3.0 2.4 0.5 1.1
3.8 3.9 3.8 3.4 3.4 2.5 1.1 1.0
3.8 3.8 3.3 3.4 3.4 2.5 1.1 1.0
Average grade is obtained by the evaluation of 4 fingermarks by two independent experts. Each value corresponds to the average obtained over the three periods of time (24 h, 7 days, 14 days) for each temperature. Final grade of the technique is the average over the three periods of time and over the three temperatures (RT, 63 8, 200 8C).
GB and CA + GB generated good contrast, but in many cases showed the inconvenience of reacting irregularly, causing incomplete or partially overdeveloped areas. Fig. 3 shows a typical case of non-uniform development by GB. A possible procedure to avoid this issue is to photograph the sample periodically during the development, recording new sections without losing the earliest ones by the overdeveloping. The final image can be constructed by overlapping successive pictures, using basic computational tools available in commercial image editing software. An unexpected phenomenon was observed in the case of GB (and CA + GB) developments on most of the discs heated to 200 8C.
In regular developments, the GB solutions react with the metallic surface making it darker while the regions protected by the fingermark ridge residues remain clear [9,22] (see Fig. 4 for disc heated to 63 8C). However, in many of the discs heated up to 200 8C the opposite effect occurred: a reverse development characterized by dark ridges and bright background. Fig. 5 shows a reverse development by GB on a disc preheated up to 200 8C. SEM images of regular and reverse developments using GB are shown in Figs. 6 and 7, respectively. In Fig. 6 the regular corrosion of the non-protected regions (valleys) is obvious, whereas in Fig. 7 the action of GB is predominantly along the ridges.
Fig. 2. Fingermarks developed on brass discs by the tested techniques (63 8C, 14 days).
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Fig. 3. Partial development by GB on a brass disc (63 8C, 24 h).
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Fig. 6. SEM image of regular GB development on brass disc.
Fig. 4. Regular development by GB on brass disc preheated up to 63 8C.
Fig. 7. SEM image of reverse GB development on brass disc.
3.2. Latent fingermarks on unfired cartridge cases
Fig. 5. Reverse development by GB on brass disc preheated up to 200 8C.
Some temperature effects on brass that can explain this phenomenon involve oxide films growth and pitting corrosion [17,26,27]. The existence of a pattern in this behavior could give rise to a new methodology of developing fingermarks on metallic surfaces subjected to heating. In addition to the suspect identification, the technique could provide relevant information, for example, on the question if the developed fingermark was deposited before or after an eventual heating of the surface.
Developments on unfired cartridge cases (control samples) are shown in Fig. 8. Different from the flat brass discs, it was not possible to visualize latent fingermarks on cartridge cases without the application of some enhancement technique. The visualization of fingermarks in cartridge cases only by the application of oblique light from common flashlights is more complicated due to the cylindrical shape and the surface conditions of the cartridge cases. CA + RP and CA + MP presented good results for relatively fresh fingermarks (24 h and 7 days), but not so for aged fingermarks (14 d). All the other techniques developed relatively good fingermarks for the 3 elapsed times (24 h, 7 days and 14 days), including AHP1 and AHP2, which did not work well with brass discs. 3.3. Latent fingermarks on unfired cartridge cases cycled through the gun Based on the results obtained from the previous phases, the CA + GB + BY40 sequence was used to develop fingermarks on the unfired cartridge cases. The first technique applied was CA, which produced very good results for discs and unfired cartridge cases (control samples). RP could be applied after CA, since it has also produced good results and because it seems to be compatible with
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Fig. 8. Developments by all tested techniques on unfired cartridge cases (control samples) for all elapsed times (24 h, 7 days and 14 days).
the subsequent application of GB and BY40. However, as the RP results were not better than those by CA under the same lighting conditions, this step was neglected. The sequence of better graduated techniques is CA + GB, which marks the surface and thus allows the visualization of fingermarks without the need of oblique lighting. The next technique in the ranking is CA + BY40, which requires UV light to generate fluorescence of the fingermarks. The combination of these 3 compatible techniques, using
3 different lighting sources, enlarges the possibility of obtaining good results. Fig. 9 shows the cartridges that were placed directly in the barrel’s chamber and then were ejected. This process did little damage to the latent fingermarks. The latent marks in cartridges submitted to the longer cycle (involving the loading of the magazine) were more damaged than those from cartridges inserted directly in the chamber, as can be
Fig. 9. Developments by 3 successive techniques (CA + GB + BY40) on 3 different samples inserted directly into the barrel’s chamber and then ejected.
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Fig. 10. Developments by 3 successive techniques on different samples that followed the whole cycle of loading the gun and then were ejected.
seen in Fig. 10. The crushing and the overlapping of the impressions are clearly visible. Nevertheless, enough areas for identification were recovered, indicating that processes involving only friction, without firing, are not the major responsible for the high degradation of the latent fingermarks on fired cartridge cases. 3.4. Latent fingermarks on fired cartridge cases In the case of fired cartridge cases naturally handled prior to firing, sets of 20 cartridges were developed by each technique for each period of elapsed time after firing. No fingermark with Bandey’s grade equal or superior to 2 was developed on fired cartridge cases. The statistics with the average number of fired cartridge cases with grades 0, 1A and 1B is displayed in Table 2. Based on the statistics from Table 2, and considering the weights 0, 0.5 and 1.0, respectively, for grades 0, 1A and 1B, the average grades for fingermarks developed on fired cartridge cases using each technique were evaluated and are displayed in Table 3. The low values of the observed average grades indicate the significant difficulty associated with the recoverability of fingermarks from fired cartridge cases. The techniques that presented the best results involved CA, BY40 and GB, which is in agreement with refs. [6,7]. As CA protects the latent fingermarks, it is strongly recommended to make use of it before any other technique. Furthermore, the possibility of the cumulative use of CA, GB and BY40 increases the chances of obtaining good developments. Fig. 11 shows the application of this sequence to a single grade-1B fired cartridge case. Some of the best developments obtained in this phase are shown in Fig. 12. They were developed using the sequence CA + GB + BY40 and all of them presented grade 1B. The homemade formulation of AHP using household vinegar and household hydrogen peroxide presented
similar results (not shown) to those obtained from AHP1 and AHP2 formulations. As shown in Fig. 13, most of the ridge details developed were found close to the cartridge base (grade 1A). This is in accord with the results of Williams [20] and Bhaloo et al. [10]. Furthermore, a narrow zone that extends from the base to near the opening of the cartridge case can be observed in many samples, as shown in Figs. 14 and 15. This pattern was also observed by Bhaloo et al. [10]. According to those authors, this narrow zone corresponds to the surface of the cartridge case adjacent to the top of the barrel of the firearm, which does not show as much evidence of damage as its opposite side adjacent to the bottom-most part of the chamber of the firearm.
Table 3 Evaluation of average grades of the fingermarks developed on fired cartridge cases following the slightly modified Bandey’s grading scale (cf. Section 2.5). Technique
CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2
Average gradea
Total average gradeb
24 h
7 days
14 days
0.04 0.05 0.39 0.29 0.15 0.08 0.06
0.05 0.10 0.28 0.18 0.19 0.04 0.08
0.05 0.03 0.21 0.09 0.13 0.04 0.06
0.05 0.06 0.29 0.18 0.15 0.05 0.07
a Average grade obtained by two independent examiners for sets of 20 fired cartridge cases. b Total average grade obtained over the three periods of time (24 h, 7 days, 14 days).
Table 2 Statistics with the average number of fired cartridge cases (for sets of 20 samples) with grades 0, 1A and 1B evaluated by two independent experts following the slightly modified Bandey’s grading scale (cf. Section 2.5) for each period of elapsed time after firing. Technique
24 h 0
1A
1B
0
1A
1B
0
1A
1B
CA + RP CA + MP CA + GB CA + BY40 GB AHP1 AHP2
18.5 18.0 9.5 11.0 15.5 17.5 17.5
1.5 2.0 5.5 6.5 3.0 2.0 2.5
0.0 0.0 5.0 2.5 1.5 0.5 0.0
18.0 17.0 12.0 15.0 14.5 18.5 17.5
2.0 2.0 5.0 3.0 3.5 1.5 2.0
0.0 1.0 3.0 2.0 2.0 0.0 0.5
18.5 19.0 14.0 17.5 16.0 18.5 18.0
1.0 1.0 3.5 1.5 3.0 1.5 1.5
0.5 0.0 2.5 1.0 1.0 0.0 0.5
7 days
14 days
Fig. 11. Application of the sequence CA + GB + BY40 to a single fired cartridge case.
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Fig. 12. Some of the best developments on fired cartridge cases of different ages naturally handled before firing. They were developed using the sequence CA + GB + BY40 and all of them were graded as 1B.
Fig. 13. Grade 1A typical developments indicating the base of the fired cartridge cases as the richest minutiae area.
Fig. 14. CA development pattern seen in 3608 showing a narrow zone that extends from the base to near the opening of the case.
4. Discussion The visualization of fingermarks on planar metallic surfaces without the application of developers, only using oblique lighting, can be explained by optical interference of the light [29]. This resource was successfully used to visualize fingermarks on flat brass discs, but did not work so well for brass cartridge cases using common flashlights, probably because of the cylindrical shape and surface conditions of the cartridge cases.
The performed experiments demonstrated that heated brass discs do not accurately reproduce the effects of real firing over latent fingermarks on fired cartridges surfaces. The heat treatments of the discs described in Section 2.2 (simulating the real maximum temperatures achieved by the external surfaces of fired cartridges) did not prevent the visualization of the latent fingermarks, in agreement with previous reports by Migron et al. [30], and Wiesner and Springer [31].
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Fig. 15. GB development pattern seen in 3608 showing a narrow zone that extends from the base to near the opening of the case.
Likewise, the frictions experimented by the unfired cartridges going through the gun parts (without firing) did not cause significant damage to the latent fingermarks as the global effects generated by firing, corroborating the conclusions of Wiesner and Springer [31]. Therefore, other factors besides temperature and pure friction act over the cartridges during firing, causing the effects observed in Section 3.4. Three possible factors can be responsible for the damages caused to the latent fingermarks on fired cartridges [6,12,31]: (1) The blowback of the hot gases produced by the propellant burning, which wipes great part of the lateral surface of the cartridge, once the barrel’s chamber is not perfectly sealed and may leave some looseness between the cartridge and the chamber; (2) The expansion of the cartridge due to the elevated internal pressure, which maximizes the friction between the lateral surface of the cartridge and the chamber during the ejection. As the thickness of the cartridge wall is smaller next to the opening and reinforced next to the base, this last region tends to suffer less expansion, justifying the predominance of ridge details found closer to the cartridge base. (3) The influence of the propellant byproducts brought by the blowback of gases, generating coatings that may affect development and visualization of latent fingermarks. These factors cause noticeable differences between the simulations without firing and the tests with firing and may depend on the gun and ammunition characteristics, such as caliber, type and geometry of the chamber, amount and composition of the propellant [6,10]. In addition to these factors related to the firing process, it is also possible that brass discs might be different in both chemical composition and surface condition from commercially manufactured cartridge cases. This could explain, for example, the discrepancy between the poor results for AHP developments on unheated brass discs (Table 1) and the good results obtained for unfired cartridge cases using the same techniques (Fig. 8). The reverse development by GB seen in brass discs heated up to 200 8C was not observed in fired cartridges. It can be thought as further evidence that the external surfaces of the fired cartridge cases do not reach temperatures as high as 200 8C, in according with conclusions of Gashi et al. [25].
5. Conclusions Among the tested techniques, those that showed the best consistency considering the results for both fired and unfired cartridge cases were CA, GB and BY40. The compatibility between them, which use different lighting sources, allows a combined use, increasing the possibility of obtaining better results. The suggested sequence is CA + GB + BY40, for both fired and unfired cartridge cases. The isolation of the loading and ejection processes indicated that friction inside the gun without firing does not cause significant damage to the fingermarks. Good state fingermarks were developed on unfired cartridge cases cycled through the gun. The firing effects over the fired cartridge cases resulted in significant loss of ridge details. The richest minutiae area was generally located next to the base. The patterns observed on the latent fingermarks recovered from fired cartridge cases indicate that the success in developing this kind of evidence depends not only on the techniques employed, but on a sum of factors. It is necessary that good fingermarks are produced, neither damaged nor overlapped during insertion in the magazine. These latent marks must be localized at the small regions that will survive from firing and ejection, and should present enough minutiae to allow comparison and individualization. Acknowledgements The authors would like to thank the National Institute of Identification of the Federal Police Department of Brazil (INI/ DIREX/DPF), in special the fingermark experts Eulemar Amorim and Luciene Marques for valuable help during the work. We also thank the Brazilian Association of the Federal Police Fingermark Experts (ABRAPOL) and the Brazilian agencies CAPES, CNPq, FAPES and FINEP for the partial financial support. References [1] J.W. Bond, D. Phil, B.A. Chuck Heidel, Visualization of latent fingerprint corrosion on a discharged brass shell casing, J. Forensic Sci. 54 (4) (2009) 892–894. [2] H.N. Freeman, Magnetic fingerprint powder on firearms and metal cartridges, J. Forensic Ident. 49 (5) (1999) 479–484. [3] S. Johnson, Development of latent prints on firearms evidence, J. Forensic Ident. 60 (2) (2010) 148–151. [4] A. Pratt, Fingerprints and firearms, J. Forensic Ident. 62 (3) (2012) 234–242. [5] B. Maldonado, Study on developing latent fingerprints on firearm evidence, J. Forensic Ident. 62 (5) (2012) 425–429. [6] R.K. Bentsen, J.K. Brown, A. Dinsmore, K.K. Harvey, T.G. Kee, Post firing visualisation of fingerprints on spent cartridge cases, Sci. Just. 36 (1) (1996) 3–8.
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