Variation of the chemical contents and morphology of gunshot residue in the surroundings of the shooting pistol as a potential contribution to a shooting incidence reconstruction

Forensic Science International 210 (2011) 31–41

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Variation of the chemical contents and morphology of gunshot residue in the surroundings of the shooting pistol as a potential contribution to a shooting incidence reconstruction Zuzanna Broz˙ek-Mucha a,b,* a b

Institute of Forensic Research, Westerplatte St. 9, 31-033 Krakow, Poland Jagiellonian University, Faculty of Chemistry, Ingardena St. 3, 30-060 Krakow, Poland

A R T I C L E I N F O

A B S T R A C T

Article history: Received 28 September 2010 Received in revised form 17 January 2011 Accepted 25 January 2011 Available online 26 February 2011

A study of the chemical contents and sizes of gunshot residue originating from 9  18 mm PM ammunition, depositing in the vicinity of the shooting person was performed by means of scanning electron microscopy and energy dispersive X-ray spectrometry. Samples of the residue were collected from targets placed at various distances in the range 0–100 cm as well as from hands and clothing of the shooting person. Targets were covered by fragments of white cotton fabric or black bovine leather. In the case of cotton targets microtraces were collected from circles of 5 and 10 cm in radius. Results of the examinations in the form of numbers of particles, proportions of their chemical classes and dimensions revealed a dependence on the distance from the gun muzzle, both in the direction of shooting and in the opposite one, i.e., on the shooting person. The parameters describing gunshot residue differed also depending on the kind of the target substrate. The kind of obtained information gives rise to understanding the general rules of the dispersion of gunshot residue in the surroundings of the shooting gun. Thus, it may be utilised in the reconstruction of shooting incidences, especially in establishing the mutual positions of the shooter and other participants of the incident. ß 2011 Elsevier Ireland Ltd. All rights reserved.

Keywords: Forensic science Gunshot residue Scanning electron microscopy and energy dispersive X-ray spectrometry Distribution of properties of particles depending on the shooting range Crime reconstruction

1. Introduction The most frequent aspects of firearm-related investigations are the following: detection and analysis of gunshot residue originating both, from the primer and from the propellant, identification of bullet entry holes and shooting distance estimation, linking weapons and parts of fired ammunition with gunshot entries, detection of firearm imprints on the hands of suspects [1]. However, despite the rapid developments in methods of instrumental analysis and useful protocols being recently worked out by forensic chemists, there still remain challenges such as establishing the mutual position of persons involved in a shooting incident. Gunshot residues (GSR), originating from the primer of firearm ammunition are valuable evidence in cases of shooting. For the purpose of proving that a person was present in a close vicinity of a firing gun, GSR ought to be characterised by both, the specific element content being related mainly to the composition of the primer mixture and their morphology of molten and suddenly cooled droplets of metals revealing sizes in the range from sub-

* Institute of Forensic Research, Department of Criminalistics, Westerplatte St. 9, 31-033 Krakow, Poland. Tel.: +48 12 422 87 55x185; fax: +48 12 422 38 50. E-mail address: [email protected]. 0379-0738/$ – see front matter ß 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2011.01.031

micrometers to several micrometers. The most popular method simultaneously providing information on the two features is scanning electron microscopy combined with energy dispersive Xray spectrometry (SEM-EDX) [2–6]. Automation of the analytical process of GSR examinations with this method was successfully solved helping an operator in the arduous process of location and chemical classification of particles [7]. Contemporary SEM-EDX systems are able to detect submicron particles and the quality of their performance in GSR search can be measured by means of artificial test sample fulfilling the requirements of standards ISO 5725 and ISO 13528 [8]. The administration of justice frequently asks about the shooting distance, the type and calibre of gun and ammunition, the details of the relative positions of people involved in a crime and finally the reconstruction of the course of an incident. A considerable number of these cases still concerns using Makarov type of pistols and ammunition. In 1951 the pistol of Makarov (PM) was chosen to be an official weapon of Soviet military and police and its Eastern European satellites and still remains the service pistol of Russian military and police service as well as in many Eastern European Countries and former Soviet Republics, despite of successive replacing them by modern 9 mm Luger parabellum types of hand guns. Today, the Makarov is a popular handgun for concealed carry in the United

32

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

States. Variants of the pistol remain in production in Russia, China and Bulgaria. The smallest hand gun utilising Makarov ammunition (also called 9  18 mm PM) was invented in Poland and has been manufactured at the F.B. Radom plant as the P-64, with 190,000 made between 1966 and 1977 for police and army. Its later modification, called P-83 was also accepted into the inventory of the Polish Army and Ministry of Internal Affairs in 1984 and manufactured until year 2000. In 2002 Polish Police and Army have introduced an ultra-modern P-99 polymer-framed semiautomatic pistol designed by the German company of Carl Walther Waffenfabrik of Ulm, 9 mm Luger calibre, in order to successively replace the service weapon with the one compatible with NATO standards, although, as of 2010 large numbers of P-64 and P-83 are still in Military and Police service in Poland, similarly to situation in other countries of Europe, Asia and America. The appropriate ammunition has been also produced in Poland at Mesko Metal Works, Skarzysko-Kamienna. It was observed that 9 mm Makarov ammunition of this manufacturer produces none or very small numbers of the particles simultaneously containing lead, antimony and barium being characteristic gunshot residue [9–12]. Although this property was found to be interesting for distinguishing them from GSR originating from other types of ammunition [13–17], it always caused difficulties in the interpretation of the results of GSR examinations obtained for samples collected from suspect’s hands taking into account the formal approach of the evaluation of GSR. As the formal scheme of data interpretation underestimates the evidential value of GSR originating from ammunition other than traditionally primed with lead, antimony and barium compounds, another approach, called ‘‘case-to-case’’, was suggested by Romolo and Margot [18] and adopted by many experts. An individual treating of a case requires not only utilisation of information included in case files, e.g., the autopsy report, but also a knowledge on the spatial expansion of GSR originating from certain type of gun and ammunition used in the crime scene. The majority of studies on the spatial expansion of GSR performed so far concerned their presence at certain distances from the shooting gun [19]. An interesting idea on the distribution of numbers of characteristic particles in the surroundings of the shooting person was assembled performing single experiments in controlled conditions, including preparation and distribution of horizontal accumulating targets around the shooter at various heights [20]. An attempt was also done to extract information on various features of gunshot residue originating from a 9 mm Luger ammunition and deposited on materials being normally obtained as evidence: the shooter’s hands and clothing as well as the victim’s clothing that acted as vertical targets. Distribution of particles on targets and on the shooting person, i.e., hands and the forearm, arm and back parts of the upper clothing revealed a significant dependence on the shooting distance. It has been found that numbers of particles, the mutual proportions of their chemical classes and their sizes varied with the distance from the shooting gun [21]. Moreover, the mutual proportions between lead particles originating from the bottom of the projectile and antimony particles originating from the primer have shown the opposite course of changes. Rijnders et al. also studied GSR samples taken from seven different locations around and in the firearm using SEM-EDX method. For the same ammunition they found high correlations between samples taken from external positions (such as hands of shooter, bullet-entrance holes) but poor correlation between internal samples (such as firearm barrel, cartridge case) and external samples. A high degree of association was found between samples that simulated victim and shooter. They concluded that GSR comparison studies are meaningful but care needs to be taken when choosing suitable exhibits. External samples (such as hands of shooter, bullet-entrance holes) are more

suitable candidates than internal samples (barrel of the firearm, cartridge case) for evidence material [22]. In opposition to the opinion of Rijnders et al. [22], the author of the current work recons that examination of GSR originating from the cartridge cases are always very informative and important evidence material, even when great differences occur in comparison to the airborne GSR. That has been supported by a comparative study of the chemical contents and morphology of airborne particles and these taken from inside the cartridge case published elsewhere [23]. The distribution of the chemical elements in the gunshot residue is determined by two main factors: the direction of the movement of the expanding products of the burning propellant at the stage of internal ballistics and subsequent interactions with the materials that were applied to construct the gun and ammunition. Whereas the elemental contents of the residue present inside the cartridge case resembles the primer composition, the particles leaving the gun muzzle are usually enriched with material originating from the other parts of a cartridge: the case, the bullet core and jacket and the debris deposited on the internal walls of the muzzle. The subsequent phenomena taking place during cartridge discharge, being very dynamic and complex in nature, were so far rare subject of studies performed by GSR examiners for better understanding their dispersion in the vicinity of the shooting gun. Basu made inferences on a three-stage combustion process of the primer and the propellant taking into account the morphology of GSR collected from the shooter’s hands and distributions of lead, antimony and barium in the cross-sections of particles by means of SEM-EDX, as well as the temperatures of melting and evaporation of these metals [24]. Studying GSR collected from shooter’s hands with the use of ammunition, fabricated by addition of various metals or metal compounds to the propellant or the projectile, Wolten et al. have found that materials of the projectile (e.g., lead and copper) clearly contributed to the metallic GSR. However, their quantity depended on the melting and evaporation temperatures as well as the chemical affinity of metals originating from the primer to lead and copper of the projectile core and jacket, and so the possibility of constituting alloy systems [25]. Bhattacharyya presented theoretical modelling of the phenomenon of GSR deposition on targets in the closerange shooting distances adopting the kinetic theory of gases and considering discharge products as a gaseous system that moves with a high velocity in the direction of shooting, in which the particular velocities of the constituent particles reveal a Maxwellian distribution [26]. However, the presented model did not reproduce analytical data in the form of concentration of antimony on the subsequent targets; neither did the model later modified for collisions of the metallic and the air particles [27]. The observed differences between the measured and the calculated concentrations of antimony increasing with the shooting distance may have resulted from the variation of shapes, sizes and mass of particles that were not taken into account in the model as well as a possible range of particle velocity affecting the adhesion of a particle to the target. Particles of both, lower and higher velocity than this range would not adhere to the target or reflect from it. In this view the only attempt to recognize variation of the chemical contents of GSR particles with the distance from the firing gun, both in the direction of shooting and the opposite one was demonstrated in publication [21]. The obtained results revealed their importance as potential contribution to reconstruction of mutual positions of the shooter and other persons present at the crime scene. In spite of growing interest in distribution of GSR, among other burning questions related to GSR examination reviewed recently by Dalby et al. [28], any solution to this forensic problem has not been approached before.

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Thus following work [21] the current study was undertaken to obtain information on the properties of GSR particles originating from 9 mm Makarov ammunition and deposited on various substrates and locations in the vicinity of the shooting gun with the expectation that the variations in gunshot residue compositions would support a reconstruction of shooting incidents with the use of this type of ammunition. 2. Materials and methods The subjects of the study were inorganic gunshot residues collected from various locations on the shooter and from targets placed at the distances in the range 0– 100 cm. The samples were obtained in result of two types of experiments performed in three rounds each, using the same gun and ammunition, i.e., P-64 pistol and 9 mm Makarov ammunition of Polish production. In the first experiment GSR were collected from fragments of white cotton fabric and black bovine leather. A single shot was made to a target covered with a piece of brand new material from the following distances: 0, 1, 3, 5, 10, 20, 30, 50, 70 and 100 cm. Microtraces were collected from circles of 5 cm and 10 cm in radius around the hole in the target, pressing 12 times an aluminium stub covered with an adhesive tab to its surface. In the second experiment samples of GSR were collected immediately after shooting from the shooter’s hands and later from his upper clothing, i.e., lab coat made of cotton fabric, from the following locations: lower part of the sleeves, upper parts of the front and the upper part of the back. Stubs were pressed about 100 times to the examined surfaces. Each of the test shots was done to cotton targets placed in the distance of 50 cm. Both experiments were performed in a police shooting gallery with a P-64 pistol (‘Archer’ – Radom Arms Factory LLC, Poland). Prior to the experiment the gun was cleaned with a cleaning-brush and cloth wetted in petroleum spirits away from the shooting gallery. Ammunition 9 mm Makarov FMJ (full metal jacket) manufactured by ‘Mesko’ Metal Works, Skarz˙ysko-Kamienna, Poland was applied in the experiments (production lots 2003 and 2004). All samples were collected using aluminium stubs with conductive carbon adhesive tabs by TAAB Laboratories Equipment Ltd., Great Britain. Stubs with the collected particles were covered with the conductive layer of carbon using a SCD 050 sputter, BAL-TECH, Lichtenstein to avoid charging of organic debris such as hair, fragments of epithelium, cotton fibres, particles of unburned propellant. The prepared samples were placed inside the sample chamber of a scanning electron microscope JSM-5800, Jeol with an energy dispersive X-ray spectrometer Link ISIS 300, Oxford Instruments Ltd. (Si(Li) detector, ATW – atmospheric thin window, resolution 131 eV for MnKa at 10,000 counts). The automatic identification of GSR – was performed with a GunShot program, i.e., an application of the Link ISIS 300, Oxford Instruments. The program automatically searches for particles of defined features subsequently analysing rectangular frames, into which the whole area of a stub is being divided; the number and the size of frames depends on the applied magnification. The initial setting of the program embraces defining the positions of the stubs as well as the Mn–Pd standard to establish the range of the back-scattered electron signal, the expected chemical classes of the particles, the limits of particle size and their number within a frame have to be established. The chemical classes of particles are defined by setting the list of contributing elements within broad ranges of their composition, typically between 0 and 100%. The measurement setting aimed at particles of 1 mm in diameter not to be missed (Table 1).

Table 2 Numbers of the metallic particles revealed by means of SEM-EDX method in chosen samples collected from cotton targets in the circle of 10 cm around the hole (experiment 1) and from the shooting person (experiment 2). Distance s (cm) Experiment 1 10 (target) 20 (target) 30 (target) 70 (target) 100 (target) Experiment 2 90 (back) 70 (front) 30 (sleeves) 10 (hands) 50 (target)

Sets of data containing information on the particles content, size, stage coordinates, shape factor etc., were obtained as a result Table 1 Analytical conditions of the automatic search for GSR by means of SEM-EDX method. Automatic search

GunShot, Oxford Instruments Ltd.

Magnification Accelerating voltage Working distance Acquisition time for single particle Minimum size of the particle Size of the scanned frame Height Width Area

200  20 kV 10 mm 5s 1 mm 514 mm 658 mm 0.338 mm2

Round 1

Round 2

Round 3

5912 8559 3652 856 367

5629 8332 3521 861 305

5675 8618 3428 771 306

24 38 61 2866 2337

22 110 211 3559 2790

30 44 61 1902 2910

of the automatic search of the whole area of the samples taken from the shooter’s hands, clothing and targets. Varying numbers of metallic particles, from several dozens to several thousands, were obtained (Table 2). To be able to compare between samples, taking into account either the size or the chemical content of particles, the numbers of particles of certain classes were transformed into the frequencies of occurrence fi expressed as fraction against the total number of the metallic particles found in a sample: N fi ¼ P i i Ni where Ni is the number of particles of i-th class. For each of the studied samples the frequencies of occurrence of the following chemical classes of particles: PbSbBa, PbBa, PbSb, SbBa, Pb, Sb(Sn) and Ba as well as the following ranges of their sizes: (0–1.00), (1.01–1.50), (1.51–2.00), . . . (6.01–7.00), (7.01– 10.00), (10.01–20.00), (20.01–30.00) mm were calculated.

cotton r = 5 cm

18000

cotton r = 10 cm 16000

leather r = 5 cm

14000 12000

N

3. Results

33

10000 8000 6000 4000 2000 0 0

20

40

60

80

100

s [cm] Fig. 1. Number of particles collected from targets depending on the shooting distance.

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holes in the cotton targets. The obtained results are presented in Fig. 1 taking into account particles of all the chemical classes. One can observe that very numerous particles are present on targets shot in the distances of 10–30 cm. Small numbers of particles can be observed for both, a contact or very close range shots as well as for the distances over 50 cm. It is remarkable that the numbers of particles revealed in samples taken from the leather targets in the range 10–100 cm at radius r = 5 cm around the hole are smaller than the ones acquired for cotton targets at both, 5 and 10 cm radiuses. Opposite to that, for the distances in the range of 0–5 cm the number of particles found for leather targets are greater than the ones observed for cotton targets. Such a behaviour can be attributed to the different kinds of the target materials; the surface of bovine leather is much more coherent and smoother than the cotton fabric. Thus, at close range targets, where the particles are expected to have the highest

The size of a particle, being automatically established by the program GunShot, is defined as an equivalent circle diameter d, according to the following formula: rffiffiffiffiffiffiffiffiffiffiffiffiffi 4area

d¼

p

and expressed in micrometers. 3.1. Distribution of GSR on targets For achieving a general view of the possible numbers of metallic GSR present on cotton and leather targets being shot at various distances, samples were collected from each target by pressing 12 times a stub from a circle of 5 cm radius around the entrance hole and additionally from a circle of 10 cm in radius around the same

a

d

0.6

0.9 0.8

0.5

0.7 0.6

0.4

f

f 0.3

0.5 0.4 0.3

0.2

0.2

0.1

0.1 0.0

0.0 PbSbBa

PbSb

PbBa

SbBa

Pb

Sb(Sn)

PbSbBa

Ba

PbSb

PbBa

Sb(Sn)

Ba

Sb(Sn)

Ba

Sb(Sn)

Ba

50 cm

10 cm 0.8

e

0.7 0.6

1.0 0.9 0.8 0.7 0.6 f 0.5 0.4 0.3

0.5 f 0.4 0.3 0.2

0.2 0.1 0.0

0.1 0.0 PbSbBa

PbSb

PbBa

SbBa

Pb

Sb(Sn)

PbSbBa

Ba

PbSb

PbBa

SbBa

Pb

Chemical class

Chemical class

70 cm

20 cm

c

Pb

Chemical class

Chemical class

b

SbBa

f

0.8 0.7

1.0 0.9 0.8 0.7

0.6 0.5

0.6 f 0.5 0.4

f 0.4 0.3

0.3 0.2

0.2 0.1

0.1 0.0

0.0 PbSbBa

PbSb

PbBa

SbBa

Chemical class

30 cm

Pb

Sb(Sn)

Ba

PbSbBa

PbSb

PbBa

SbBa

Pb

Chemical class

100 cm

Fig. 2. Chemical composition of particles collected from cotton targets, in circle of radius r = 5 cm around the hole, depending on the shooting distance.

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

velocity and so the highest momentum, it is probable that the cotton fabric behaved as a sieve letting some of particles go through, whereas in the case of leather particles were caught in the grooves. However, at the distances higher than 10 cm, where particles move with smaller velocities the cotton targets reveal greater adhesive properties most probably due to their more developed surface and more complex structure consisting of threads and fibres. Distributions of chemical classes of particles detected in samples taken from cotton and leather targets in the circle of radius r = 5 cm around the gunshot hole are presented in Figs. 2 and 3, respectively. The appearance of the appropriate charts obtained for samples collected from cotton targets at the circle of r = 10 cm in the radius around the hole and the course of changes of the mutual proportions of the classes of particles with the shooting distance were very similar to these obtained for r = 5 cm (Fig. 2), and so the results for samples collected from the circle of r = 10 cm are not presented. Among particles revealed in all the samples taken from targets, only particles of classes PbSb, Pb and Sb were observed. The primer of 9 mm Makarov ammunition by ‘Mesko’, similarly to that of 9 mm Luger by the same producer, is composed of mercury fulminate as the detonator, antimony trisulfide – the

a

fuel and potassium chlorate – the oxidizer. Due to very small amount of mercury being applied in the primer mixture as well as the volatility and reactivity of mercury, usually less than 1% of particles in each sample contained minor quantities of mercury. Particles containing only mercury or its significant amounts were not found. That remains in agreement with results of earlier studies on the chemical contents of particles taken from the cartridge case and hands of a person shooting with a Mesko 9 mm Luger ammunition [21] as well as on particles originating from 9 mm Makarov [9–12], both being mercury fulminate primed types of ammunition. As in both calibres of ammunition produced by ‘Mesko’ the primer cup is sealed with tin, in the majority of particles containing antimony also tin is present. Significant amounts of lead containing airborne particles are related to an interaction of the products of reacting primer and propellant mixtures with the lead core of the projectile that at its bottom is not covered by the copper jacket and no lead compounds were present in the primer mixture. For the same production lots of Mesko 9 mm Makarov ammunition among the residue from inside the cartridge cases no lead was found, instead the presence of sulphur, chlorine, tin, antimony, potassium and mercury were established.

d 1.0

0.9 0.8

0.9

0.7

0.8 0.7 0.6

0.6 f

35

0.5

f 0.5 0.4 0.3 0.2

0.4 0.3 0.2 0.1

0.1 0.0

0.0 PbSbBa

PbSb

PbBa

SbBa

Pb

Sb(Sn)

Ba

PbSbBa

PbSb

Chemical class

PbBa

1.0 0.9

e 1.0

0.8 0.7 0.6

0.8 0.7 0.6

f 0.5 0.4 0.3 0.2

f 0.5 0.4 0.3 0.2

0.1 0.0

0.1 0.0

Sb(Sn)

Ba

Pb

Sb(Sn)

Ba

Pb

Sb(Sn)

Ba

0.9

PbSbBa

PbSb

PbBa

SbBa

Pb

Sb(Sn)

PbSbBa

Ba

PbSb

f

1.0 0.9

1.0 0.9

0.8 0.7 0.6

0.8 0.7 0.6

f 0.5 0.4 0.3 0.2

f 0.5 0.4 0.3 0.2

0.1 0.0

0.1 0.0 PbSb

PbBa

SbBa

Chemical class

20 cm

SbBa

30 cm

50 cm

PbSbBa

PbBa

Chemical class

Chemical class

c

Pb

70 cm

10 cm

b

SbBa

Chemical class

Pb

Sb(Sn)

Ba

PbSbBa

PbSb

PbBa

SbBa

Chemical class

100 cm

Fig. 3. Chemical composition of particles collected from leather targets, in circle of radius r = 5 cm around the hole depending on the shooting distance.

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

36

In the sample collected from the cotton target placed at the distance of s = 10 cm from the muzzle, both, from the circle of r = 5 cm (Fig. 2) and of r = 10 cm around the hole, frequencies of occurrence of PbSb and Pb classes of particles are nearly 0.3 and of Sb about 0.6. They are gradually changing with the shooting distance, so that at distances of s = 70 cm and 100 cm fractions of Pb- and PbSb-particles decrease to less than 0.1, whereas the fraction of Sb-particles increases to over 0.9. In samples collected from leather targets (Fig. 3) one can observe generally smaller frequencies of occurrence of lead containing particles, starting from less than 0.2 and finishing in the sample collected from target at less than 0.1 at the distances of 70 cm and 100 cm from the muzzle. The distributions of sizes of particles collected from leather targets from circle of 5 cm in radius and from cotton targets from circles of both, 5 and 10 cm in radius, in function of the shooting distance, were all similar to each other. Thus, as an example, the frequencies of occurrence of particles of certain size range obtained for samples taken from circle of r = 10 cm around the hole in the cotton targets placed in the following distances from the muzzle: 10, 20, 30, 50, 70, and 100 cm are presented in Fig. 4. For all of the examined samples taken from the targets, the majority of particles are of the smallest size in the ranges of sub-microns to about 1.5 mm. There were not present particles bigger than 4.0–4.5 mm in the sample collected from target in the distance 10 cm. Bigger

a

particles occurred at longer distances from the muzzle. Thus the distributions of size of the particles become more flat and the relative contribution of larger particles grows with the distance from the muzzle in the direction of shooting up to the distance of the muzzle of 70 cm. At the shooting distance of 100 cm again lack of particles greater than 4.5 mm in diameter is observed. This can be attributed to a smaller load of the propellant in 9 mm Makarov ammunition in comparison to 9 mm Luger ammunition of the same type of priming, and so smaller initial particle velocity [21]. 3.2. Distribution of GSR on the shooting person Distributions of chemical classes and sizes of particles detected in the samples taken from the shooting person, i.e., his hands and clothing: the lower parts of the sleeves, the front upper parts and the back upper parts are presented in Figs. 5 and 6, respectively. The following distances (s) from the pistol muzzle to the locations at the shooting person, an adult male 185 cm tall, were assumed: hands – 10 cm, sleeves – 30 cm, the front upper part of clothing – 70 cm and the back upper part of clothing – 90 cm. The assessed values of distance were given the negative sign as they were opposite to the direction of shooting. From the inspection into distributions of the chemical classes of particles collected from the shooter’s clothing (Fig. 5b–d), one can find the prevailing, nearly equal amount of Sb- and Pb-particles,

d

0.50 0.45 0.40 0.35 f 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2 . 51 5 3 . - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4 . - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6 . 01 0 7 . - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 0 1 -2 0. 0

0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2. 51 5 3. - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4. - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6. 01 0 7. - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 0 1 -2 0. 0

f

0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00

d [µm]

d [µm]

70 cm

10 cm

e

b 0.45

0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2. 51 5 3. - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4. - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6. 01 0 7. - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 0 1 -2 0. 0

0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2. 51 5 3. - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4. - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6. 01 0 7. - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 0 1 -2 0. 0

0.40 0.35 0.30 0.25 f 0.20 0.15 0.10 0.05 0.00

0.40 0.35 0.30 f 0.25 0.20 0.15 0.10 0.05 0.00

d [µm]

d [µm]

50 cm

30 cm

f

c 0.45

0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2. 51 5 3. - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4. - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6. 01 0 7. - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 1 0 -2 0. 0 d [µm]

20cm

0. 01 1. - 1. 01 0 1. - 1. 51 5 2. - 2. 01 0 2. - 2. 51 5 3. - 3. 01 0 3. - 3. 51 5 4. - 4. 01 0 4. - 4. 51 5 5. - 5. 01 0 5. - 5. 51 5 6. - 6. 01 0 7. - 7. 01 0 8. - 8 01 .0 10 - 1 .0 0. 0 1 -2 0. 0

0.50 0.45 0.40 0.35 0.30 f 0.25 0.20 0.15 0.10 0.05 0.00

0.40 0.35 0.30 f 0.25 0.20 0.15 0.10 0.05 0.00

d [µm]

100 cm

Fig. 4. Size of particles collected from cotton targets (r = 10 cm) depending on the shooting distance.

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

a 0.45 0.4

1 0.9 0.8 0.7 0.6 f 0.5 0.4 0.3 0.2 0.1 0

0.35 0.3 0.25 f 0.2 0.15 0.1 0.05 0

PbSbBa

PbBa

PbSb

SbBa

Pb

0. 01 1. 1.0 01 1. 1.5 51 2. 2.0 01 2. 2.5 51 3. 3.0 01 -3 3. 51 .5 4. 4.0 01 -4 4. 51 .5 5. 5.0 01 -5 5. 51 .5 6 . 6.0 01 7 . 7.0 01 8. - 8 01 .0 10 - 1 .0 0.0 1 -2 0. 0

a

Sb

d [µm ]

chemical class hands (-10 cm)

hands (-10cm)

1.00

b

0.45 0.4 0.35 0.3 f 0.25 0.2 0.15 0.1 0.05 0

0.80 0.60

f 0.40 0.20 0.00 PbSb

SbBa

Pb

Sb

-1

PbBa

0. 01

PbSbBa

1. 01 .0 1. 1. 5 51 2. 2. 0 01 2. 2. 5 51 3. 3. 0 01 3 . 3 .5 51 4 . 4 .0 01 4. 4. 5 51 5. 5. 0 01 5. 5. 5 51 -6 6. 0 1 .0 7 . - 7 .0 01 8. - 8 01 .0 10 - 1 .0 0.0 1 -2 0. 0

b

37

chemical class sleeves (-30cm)

d [µm ]

c

sleeves (-30 cm)

0.6 0.5

c

0.4

f 0.3 0.2 0.1 0 PbSbBa

PbBa

PbSb

SbBa

Pb

Sb

d

0. 01 1. 1. 0 01 1. 1. 5 51 2. 2. 0 01 2. 2. 5 51 3. 3. 0 01 3. 3. 5 51 4. 4. 0 01 -4 4. 51 . 5 5. 5. 0 01 -5 5. 51 . 5 6. 6. 0 01 7. 7. 0 01 8. - 8 01 . 0 10 - 1 0. .0 0 1 -2 0. 0

chemical class front (-70 cm)

0.4 0.35 0.3 0.25 f 0.2 0.15 0.1 0.05 0

0.6

d [µm ]

0.5

front (-70 cm)

0.4

d

f 0.3

0.4

0.35 0.3 0.25 f 0.2

0.1 0 PbSbBa

PbBa

PbSb

SbBa

Pb

Sb

chemical class back (-90 cm)

Fig. 5. Chemical composition of particles collected from the shooter depending on the distance from the muzzle.

small amounts of PbSb-particles, being similar to the distributions of target samples and some minor quantity of particles of other classes. However, distribution of the chemical classes of particles collected from the shooter’s hands, differs significantly: the Sb class outnumbers the other six classes of particles (Fig. 5a). The presence of minor quantities of barium containing particles in samples taken from the shooters hands and clothing does not originate from the primer or the propellant. These particles may have originated from the barrel contaminated with previous shootings, possibly with other kinds of ammunition, since there are no perfect methods of cleaning the weapon from the GSR [29].

0.15 0.1 0.05 0 0. 01 1. 1. 0 01 1. 1. 5 51 -2 2. 01 . 0 2 . 2 .5 51 3 . 3 .0 01 -3 3. 51 . 5 4. 4. 0 01 4. 4. 5 51 5. 5. 0 01 5. 5 .5 51 6 . 6 .0 01 7. 7. 0 01 8. 01 8. 0 10 - 1 . 0 0 .0 1 -2 0. 0

0.2

d [µm ]

back (-90 cm) Fig. 6. Size of particles collected from the shooter depending on the distance from the muzzle.

Analyzing the distribution of sizes of particles collected from the shooting person in Fig. 6 one can find that for all of the examined samples the majority of particles are of the smallest size in the ranges of sub-microns to about 1.5 mm, similarly as in the case of targets. The distributions of size of the particles become more flat and the relative contribution of larger particles increases

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

38

fi

-110 -90

-70

-50

-30

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -10

PbSb

P

Pb Sb(Sn)

10

30

50

70

90

11 0

s [c m] Fig. 7. Mean values of frequencies of occurrence of particles of the chemical classes PbSb, Pb and Sb(Sn) in the dependence on the distance s from the gun muzzle.

with the distance from the muzzle in the opposite direction to shooting, up to the distance of s = 70 cm, i.e., the front upper part of the shooter’s clothing. In the case of the back upper part of the shooter’s clothing (s = 90 cm) no particles of greater size than 4.5 mm are present. This fact, similarly to that observed in the case of targets, supports the inference that the range of particles depends on the calibre and propellant load of ammunition. 3.3. Combined inspection into the chemical contents and size of GSR depending on the distance For an overlook of the properties of particles in function of the distance from the gun muzzle their mean values were calculated taking into account three rounds of the performed experiment. The frequencies of occurrence of particles of the major chemical classes: PbSb, Pb and Sb depending on the shooting distance are

di 2.4 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -110 -90 -70 -50 -30 -10 10

a

PbSb Pb Sb(S n)

30

50

70

90 110

s [c m]

b

presented in Fig. 7. Mean values of the diameters of particles for each of the major chemical classes of the particles present in each location as well as for the entire population of particles detected for certain location were calculated according to the following formula:

3.0 2.5

hdi ¼

j

dj

N

where dj is the diameter of the j-th particle (mm), N is the number of particles of chosen chemical class of particles in certain location (or the entire population of particles found for a location). Except for PbSb class the size of particles significantly differ from those in the opposite direction (Fig. 8a). It can be seen in Fig. 8b that the mean values of the equivalent circle diameter of all particles increase with the distance from the muzzle in the direction of shooting from the value of about 1.25 mm at the distance of 10 cm from the muzzle to 1.75 mm at the distance of 70 cm and remain at the same level of about 2.0 mm for all locations on the shooting person. That shows that there is a relatively greater contribution of larger particles in the population of particles collected from the shooting person, i.e., in the direction opposite to shooting. A large value of the mean diameter of particles collected from the shooter’s hands (s = 10 cm), can be related to the fact that a significant amount of GSR escaping from the ejection port contribute to the population of the GSR depositing on hands. Moreover, relatively large particles are being formed in the region of back parts of the gun, similarly to these observed inside the cartridge case. It might be so due to more likely condensation processes in the limited space prior to cooling in the air. Unlike in the case of the studied 9 mm Makarov ammunition mean values of the diameter of particles observed on the shooting person with 9 mm Luger [21] increase with the distance from the muzzle up to the value of 2.82 mm that was observed for the back parts of the shooters clothing (s = 90 cm), however with a great standard deviation resulting from rather poor statistics of the low numbers of particles found in this place. Among particles of the same density the greatest kinetic energy would have those of bigger sizes. That could also partially explain the presence of rather large particles, if any, in further distances from the shooting gun in the direction opposite to shooting. It has been shown by Schwoeble and Exline [19] that the deceleration of a particle depends reciprocally on its density r and its diameter d. The diameters of the particles as well as the chemical classes assigned to them are present in the output of a GSR searching program. Thus, their density was estimated from the densities of the contributing elements in solid state, being available in the physical tables [30], and listed in Table 3. The following assumptions were made in order to simplify the calculations: all particles were of spherical shape (that remains in agreement with the observation that as much as 70% of metallic particles are of spherical shape, see e.g. [3]), they revealed homogenous chemical content and the density of particles

2.0 1.5 Table 3 Estimated densities of particles of the chemical classes found in the samples.

1.0 0.5 -110 -90

-70

-50

-30

0.0 -10 10

30

50

70

90

110

s[cm] Fig. 8. Mean values of the equivalent circle diameter of particles calculated for particles of the chemical classes PbSb, Sb(Sn) and Pb (a) and for the entire population of particles in a sample (b) in the dependence on the distance s from the gun muzzle.

Chemical class

r (g/cm3)

PbSbBa PbSb PbBa SbBa Pb Ba Sb(Sn)

7.22 9.02 7.48 5.16 11.34 3.62 6.62

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

a

ξi

0.14

39

Moreover, the weighted mean value of j was calculated for the entire population of particles in a sample according to the following formula:

0.12 0.1 0.08 PbSb

0.06

-11 0 -90

-70

-50

0.04

Pb

0.02

Sb(Sn)

0 -30 -10

10

30

50

70

90

110

s [c m]

<ξ> 0.14

b

0.12 0.10 0.08 0.06 0.04

-110

-90

-70

-50

-30

0.02 -10

10

30

50

70

90

110

s[cm] Fig. 9. The weighted mean value of j (cm3/(g mm)) calculated for particles of the chemical classes PbSb, Sb(Sn) and Pb (a) and for the entire population of particles in a sample (b) in the dependence on the distance s from the gun muzzle.

composed of more than one element was an average value of densities of the constituting elements. Therefore, similarly as in article [21], for each location studied and each of the chemical class of particles parameter j, being a reciprocal value of multiplication of the particle diameter and its density was calculated:

ji ¼

  1 cm3 ri di g mm

where ri is the mean density of a particle in the i-th chemical class (g/cm3), di is the mean value of diameters of particles in the i-th chemical class (mm).

hji ¼

i¼7 X

ji f i

i¼1

where: ji is the parameter j of the i-th chemical class of particles in a sample, fi is the frequency of occurrence of particles of i-th chemical class. In the case of the repeated experiments an average value and the standard deviation were calculated and presented in Fig. 9. With so calculated parameter an overall picture of dispersion of GSR particles was achieved. It shows that particles travelling along the shooting direction experience a slightly higher retardation than these moving in the opposite direction. Parameter hji and so the retardation of particles decreases with the distance in both directions. This trend reflects an increase of the average diameter of particles hdi as well as the change of the mutual proportion of the particles of the chemical classes, especially the rate of antimony and lead containing particles (Figs. 7 and 8). Evaluation of the repeatability of parameters describing GSR collected in the vicinity of the shooting gun. The repeatability of the results obtained from three rounds of the test shooting series, while a person was shooting to a target at 50 cm distance was evaluated. The following parameters: the number of the revealed particles, the frequencies of occurrence of their chemical classes, the equivalent circle diameters as well as parameter j that binds the size and the density of particles together with their mean values and the relative standard deviations (RSD) were calculated. Examples of the calculations for chosen parameters are presented in Table 4. Due to the complexity and dynamics of a single shot the number of particles in a sample is not a repeatable parameter and so, the RDS may take values higher than 50%, whereas RSD of the frequencies of occurrence of particles of certain class, e.g., the chemical class Sb(Sn), the mean values of particle diameters within a sample hdi and the weighted mean parameter hji were typically about 30% and less. Thus, parameters describing GSR particles originating from certain make and party of ammunition are worthwhile inspecting to obtain a meaningful description of the dispersion of particles in

Table 4 Mean values and the relative standard deviations RSD for the number of particles, frequency of occurrence f of Sb(Sn) particles, the mean diameter hdi and mean parameter hji. Parameter

Sample

Round 1

Round 2

Round 3

Mean value

RSD (%)

Number

Back Front Sleeves Hands s = 50 cm

24 28 61 2866 2337

22 110 211 3559 2790

30 44 61 1902 2910

25 61 111 2776 2679

13.4 58.5 63.7 24.5 9.2

Frequency of occurrence f Sb(Sn)

Back Front Sleeves Hands s = 50 cm

0.289 0.427 0.356 0.697 0.743

0.549 0.545 0.867 0.898 0.7036

0.468 0.356 0.560 0.818 0.7321

0.435 0.443 0.594 0.804 0.726

25.0 17.6 35.3 10.3 2.0

Mean diameter hdi (mm)

Back Front Sleeves Hands s = 50 cm

1.917 2.034 2.133 1.841 1.480

1.929 1.868 1.758 1.883 1.517

1.883 1.830 2.156 2.034 1.507

1.910 1.911 2.016 1.919 1.502

1.2 5.7 11.1 5.3 1.3

Mean parameter hji (cm3/(g mm))

Back Front Sleeves Hands s = 50 cm

0.083 0.086 0.086 0.125 0.091

0.093 0.106 0.139 0.130 0.085

0.091 0.106 0.089 0.123 0.083

0.089 0.099 0.105 0.126 0.086

6.0 11.7 28.7 2.9 5.0

40

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the vicinity of the shooting gun. The possibility of differentiation between populations of particles distributed in front of the shooting gun from these distributed behind the gun, i.e., on the shooter, may contribute to establishing the role of persons present in the crime scene at the instant of shooting and to reconstructing their positions. 4. Discussion Results presented in the current work on distribution of GSR originating from 9 mm Makarov, FMJ, ‘Mesko’ in the surroundings of the shooting gun generally resemble these obtained earlier for 9 mm Luger of the same make and type of primer [21] and highly support the inferences on the mechanism of dispersion of GSR made in this publication. Although produced contemporary, both of them represented the old-type primer mixture, based on mercury fulminate, antimony sulphide and potassium chlorate. This, however, made possible differentiation between the primer residue from those originating from the projectile, manufactured of lead core and copper jacket (FMJ) that lives uncovered the bottom, hollow part of the projectile core. Moreover, the debris containing barium that did not originated from the cartridge but from the weapon barrel, was utilized in drawing conclusions on the mechanism of GSR dispersion. The majority of the primer particles, i.e., Sb(Sn), move together with the main and the fastest stream of the combustion products of both, the primer and the propellant subsequently along the cartridge case, the barrel and the air, reaching a target in close range. The head of the shock wave of the explosives, while striking the hollow bottom of the projectile locally melts it and makes the emerging lead droplets move away from the centre of the main stream of gases towards the inner surfaces of the weapon barrel. As a results of this, when the projectile leaves the barrel, the Pb particles moving in the outer, slower layer, together with those polished off the surface of the barrel, e.g., containing Ba particles, are prone to deflection from the direction at the edge of the barrel. Within the main stream moving along the barrel, the smallest of Pb and PbSb particles are pushed forward in the direction of shooting. Due to their small sizes they experience a great retardation causing their diminishing contribution to the population of particles revealed in the subsequent targets with the increasing shooting distance. Finding only very small particles in short distances, e.g., at target placed in s = 10 cm from the muzzle supports the idea of reflection of the bigger and so having the highest kinetic energy particles from the target as suggested by Bhattacharyya [26]. After the projectile leaves the barrel, the products of detonating primer and burning propellant immediately expand in all directions and experience the air resistance leading to local turbulence of gases and vapours that may be observed in films or pictures recorded using a high-speed camera [19]. In these conditions solid particles undergo rapid retardation, deflection from the initial direction of movement along the barrel and travelling in the opposite direction to shooting, i.e., behind the gun muzzle of some of them. Particles travelling in the outer layer of the combustion stream, including the ones detached from the bottom part of the projectile (Pb containing particles) and these polished off the inner surfaces of the barrel (Ba containing particles), are prone to deflection. Particles moving in the opposite direction to shooting can deposit on the shooting person. It is worthwhile mentioning that particles depositing on the shooter’s hands significantly differ from these revealed on the targets as well as on the shooter’s clothing. In the case of semiautomatic pistols such as P-64, P-83 or Walther P-99 that utilise

the pressure of the combustion products for ejection the used cartridge case and loading a new one, the majority of particles depositing on the shooter’s hands originates from the ejector. So, the particles found on the shooter’s hands are similar to the ones taken from the cartridge cases of the same batch of ammunition in the prevailing presence of Sb(Sn) particles [23]. The absence of particles containing lead and barium in the cartridge case and their presence in the sample taken from the shooting hands proves that some of the particles originate from the muzzle deposit from the previous shots. From the performed studies as well as the case experience the author recons that in the instant of shooting the number, chemical contents and morphology of particles depositing on the shooter’s hands are determined by the nearest vicinity of the sources of particles in first order, both the muzzle and the ejector, and by the individual properties of human skin in second order. In later instances after shooting, however, the properties of skin as well as the kind of performed activity proved to be more important factors than the initial number of particles related to the location of hands close to the source of GSR. Moreover, the chemical contents of particles does not influence their loss with time from various substrates [31]. Having interrogated the chemical and morphological properties of particles of two brands of ammunition in the nearest vicinity of a shooting weapon, it can be concluded that the formation and dispersion of metallic gunshot residue are not accidental and may serve to better understanding possible differences in the quantity and quality of the particles originating from physically the same cartridge but collected from various locations in the place of shooting incident. Moreover, the presented here manner of analysis of data resulted from examinations of probes such as microtraces collected from the shooter’s hands and clothing as well as the victim’s clothing can be utilised in casework in some circumstances for reconstruction of the positions of the persons taking part in the shooting incident. 5. Conclusions Results of the performed study have demonstrated that SEMEDX method being normally used for detection of characteristic gunshot residues can also be applied to obtain information on possible differences in sizes of the particles as well as the proportions of their chemical classes depending on the distance from the muzzle of a gun, both in the direction of shooting and the opposite one. In addition to the dependence on the distance from the muzzle the properties of particles are related to the kind of substrate they were collected from, the chemical composition and details of construction of the ammunition, such as the calibre and the load of propellant etc. The mechanisms of formation and dispersion of GSR, despite its being dynamic and complex, are repeatable features of discharge of a certain type of a cartridge. That gives rise to understanding more general rules of the complex process of shooting, e.g., that differences in properties of GSR collected from various substrates and locations in the shooting scene are natural consequence of subsequent interactions of the explosive mixtures with materials constituting each part of the cartridge case and the parts of weapon that are directly related to the internal ballistics. Thus, in some favourable circumstances, when a gun of interest and a load of ammunition are accessible to a forensic expert, the presented novel way of inspection into the features of the examined GSR may contribute to crime reconstruction, especially to establishing the mutual positions and possibly the roles of the persons taking part in the shooting incident.

Z. Broz˙ek-Mucha / Forensic Science International 210 (2011) 31–41

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