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The population, transfer and persistence of fibres on the skin of living subjects
Science and Justice 49 (2009) 259–264
Contents lists available at ScienceDirect
Science and Justice j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s c i j u s
The population, transfer and persistence of fibres on the skin of living subjects Ray Palmer a,⁎, Hilary J. Burch a,b,1 a b
The Forensic Science Service, Hinchingbrooke Park, Huntingdon, Cambridgeshire, PE296NU, UK Centre for Forensic Science, University of Strathclyde, Royal College, 204 George St, Glasgow, G1 1XW, UK
a r t i c l e
i n f o
Article history: Received 19 January 2009 Received in revised form 25 February 2009 Accepted 28 February 2009 Keywords: Fibres Persistence Transfer Length Skin Bathing
a b s t r a c t Fibres were transferred to the bare arms of living subjects and their persistence determined at intervals up to 24 h, during which normal daily activity was undertaken. Decay curves showed an initial rapid loss followed by an apparently exponential decay. No target fibres were found to remain after 24 h. The length distribution showed a shift towards shorter fibre lengths and the differential shedding results for a polyester/cotton mixture showed a small bias towards the retention of cotton. The population of coloured fibres on bare skin was classified according to perceived colour, length, generic class and the presence or absence of delustrant. © 2009 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction The transfer and persistence of fibres have been the subject of a number of studies and the characteristics determined for a variety of substrates [1,3,10–15,19]. The data from these studies can be helpful in formulating expectations and evaluating the findings relating to specific casework scenarios where a time-frame for contact between a victim and their assailant needs to be estimated. In many homicides, it is not uncommon for the naked body of the victim to be deposited away from the original crime scene and for trace evidence such as fibres, potentially relating to the perpetrator, to be recovered from the skin of the victim. Using pig skin as a human analogue, Krauss and Hildebrand [18] studied the persistence characteristics of fibres on skin left outdoors and exposed to the elements over time. These authors found that the number of persisting fibres depended upon on the prevailing weather conditions, such that when the combination of wind and precipitation was recorded, fibre loss increased dramatically. These experiments never showed a total loss of fibres, suggesting that due to the lack of post-transfer activity, the probability of finding fibres originating from the offender's clothing on the skin of a homicide victim, in such circumstances, is very high. A complimentary study [17] showed that even when skin is bloodstained or wet, fibres are still recoverable using tape lifts, although the efficiency of recovery is reduced.
There does however, appear to be little if any further data relating to this substrate and to the authors' knowledge, none exists relating to the transfer and persistence of fibres on the skin of live human subjects, despite the fact that this may be useful in estimating the time-frame of contact between a victim and questioned item in the above scenario. Likewise, numerous ‘background’ fibre population studies have been performed on a variety of substrates [2,4–6,7–9] which provide data useful in the assessment of the significance of matching fibres. Again, to the authors' knowledge, no such data exists relating to the skin of live human subjects, which would undoubtedly compliment any obtained from a transfer and persistence study of this substrate. 2. Aims The aims of this study were to: • Investigate the transfer and persistence of fibres on bare skin with respect to factors of fibre type, gender, differential shedding and length. • Classify the background population of fibres on bare skin, in terms of perceived colour, length, and generic type. 3. Experimental 3.1. Target fibres
⁎ Corresponding author. E-mail address: [email protected] (R. Palmer). 1 Present address: The Royal Society of Chemistry, Thomas Graham House, Cambridge, CB4 0WF, UK.
A bright-blue knitted hooded top (80% cotton, 20% polyester mixture), and a bright-pink knitted jumper (100% wool) were chosen as the target garments for the transfer and persistence experiments.
1355-0306/$ – see front matter © 2009 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.scijus.2009.02.008
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The bright colours of the garments were selected for ease of subsequent identification and counting of target fibres. Although both garments were knitted, the inside of the hooded top had a brushed texture and this surface was used for transfer experiments due to its high transfer potential. Bulk samples of fibres from each garment were mounted and examined by high power brightfield and polarised light microscopy to confirm the fibre types listed on the garment labels, as well as providing controls for comparisons with problematic target fibres. 3.2. Fibre recovery Fibre recovery was achieved by pressing high-adhesive tape (J-LAR, 72 N/25 mm, 2 cm wide) onto the skin of the subjects. These tapings were then attached to transparent A5 acetate sheets which had been appropriately labelled [15]. The taping procedure was not reported to be uncomfortable by any of the subjects, in agreement with previous studies [7,19], although some arm hairs were removed, particularly from male subjects. Tapings were examined using a low power stereomicroscope (Nikon SMZ645) and target fibres were recorded by drawing circles on the acetate sheets using a permanent marker. 3.3. Transfer and persistence (0–5 h) Subjects were asked to attend wearing clothing that exposed their upper and lower arms. These areas of skin were taped to remove any background fibres (‘blanking’) and the tapes retained. Target fibres were transferred by contact between the skin and the target garment in question. The contact involved wrapping the sleeves of the garment around the arms of the subject (see Fig. 1) and moving the sleeves along the length of each arm and over the hands. The simulated contact was standardised as far as possible for all subjects, and was intended to represent a prolonged and forceful contact. The subject's skin was then taped immediately and the number of target fibres counted to establish an initial (t = 0) value. Subjects were subjected to the transfer procedure again and asked to return after a designated time interval (from 0.5 to 5 h). Subjects were asked not to cover their skin during this time interval, as it has been shown previously that the presence of an over garment results in a more rapid loss of fibres [14]. After the designated time period had elapsed, the subjects were taped again and the number of remaining target fibres counted. A note was made of the colour and fibre content of the upper garments worn by each subject on each occasion, and a tape lift of the garment taken.
Fig. 2. Decay curves for fibres on bare skin for (a) the pink wool jumper and (b) the blue hooded top.
3.4. 24 h persistence experiments In an extension of the persistence study, target fibres were transferred to the subjects who were asked to return in 24 h. The subjects were instructed to carry out their normal activities, including bathing or showering (subjects were provided with a white cotton towel for use after bathing to speed up searching and minimise spurious blue cotton matches). Depending on the results from this aspect of the study a similar exercise was planned for a 48 h interval. Anti-contamination measures were taken during fibre recovery and included hand washing, wearing gloves and conducting the tapings in a room separate to that used for contact with, and storage of, the target garments. 3.5. Length The lengths of any recovered target fibres were estimated by comparison with a millimetre scale under a search microscope [9]. 3.6. Differential shedding The respective numbers of cotton and polyester fibres for the blue hooded top were recorded at t = 0, t = 2 h and t = 5 h. 3.7. Population study
Fig. 1. Method of fibre transfer.
The tape lifts used for the blanking process at the start of the transfer and persistence experiments were used to determine the population of coloured fibres on the bare skin of the subjects. The fibres were classified according to perceived colour (under both reflected and transmitted light), generic class, length and (in the case of man-made fibres) the presence or absence of delustrant. Fibre generic class was established using a combination of brightfield and (where appropriate),
R. Palmer, H.J. Burch / Science and Justice 49 (2009) 259–264
Fig. 3. The length distribution of the fibres transferred from the blue hooded top at t = 0 and t = 5 h.
polarised light microscopy using a Leitz Ortholux II POL-BK polarising microscope equipped with a 20-order tilting compensator to obtain birefringence values. 4. Results and discussion 4.1. Transfer and persistence (0–5 h) 48 persistence experiments were performed for the blue hooded top and 37 persistence experiments were performed for the pink wool jumper, involving intervals of 0.5, 1, 2, 3, 4 and 5 h for each garment. The decay curves for both garments are shown in Fig. 2. Both decay curves show one standard deviation limits for each time interval. 23 initial transfer experiments were performed for the blue hooded top, and the average number of blue fibres initially transferred was 245 ± 142 (range = 106–730). 21 initial transfer experiments were performed for the pink wool jumper, and the average number of pink fibres initially transferred was 133 ± 50 (range = 48–214). The difference between the initial transfer values for blue and pink garments was significant at the 5% level using standard t-testing [23]. As the same type of contact was used in both sets of experiments, these results can be attributed to the fact that the wool garment shedded less easily than the polyester/cotton garment. There was also variation within transfer experiments using the same garment by gender, with apparently fewer blue fibres being transferred to women. The difference in the number of pink fibres transferred to men and women was however, not significant at the 5% level. It is likely that the number of fibres transferred was mainly dependent on two variables; the arm surface area and the density of arm hair (the number of initially transferred fibres was consistently higher for hirsute subjects). The standard deviations are high for both garments, which is a result of several factors. Firstly, the high standard deviations reflect the variation in persistence between individuals found in this type of study. Variations in persistence are due to individual differences in skin surface texture (with more hirsute subjects being more retentive) and also variation in subject activity following the seeding [19]. Secondly, the high standard deviations reflect the inherent variability of initial primary transfer [15]. Although the simulated contact was standardised in all transfer experiments, it is impossible to produce exact duplicates in this type of study because of natural variations in the force applied during contact with the garment. It is also possible that the propensity of the garments to shed decreased with repeated use. The standard deviations are higher at the earlier time intervals because they reflect the larger experimental error when the rate of fibre loss is greatest [10]. When the rate of fibre loss is high, small timing errors are magnified.
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The overall shape of the decay curves in Fig. 2 appears exponential after an initial rapid loss. The difference in persistence between male and female subjects was not significant at the 5% level for either garment. After 5 h approximately 15% of the blue cotton and polyester fibres remained (see Differential shedding). The rate of loss of the pink wool fibres was higher however, with only 5% of fibres remaining after 5 h. The difference in rate of loss between blue and pink garments was significant at the 5% level [23]. In most of the previous persistence studies, no difference between the persistence of wool and other fibre types was reported [10,11,14,19], but the greater persistence of cotton fibres over wool fibres is not in agreement with results obtained for human head hair [15]. It has been suggested that woollen fibres might persist in human hair for longer than other fibre types, because of hair-to-hair interactions between both rough scaled surfaces [11,15]. This however, does not appear to be the case for human skin and may be related to the difference in hair morphology, density and surface area from head hair. During some persistence experiments, subjects were required to wear a lab coat as part of their normal daily activity (white 35% cotton and 65% polyester) over the areas of skin to which the fibres were transferred. When subjects were subsequently taped, only 20% of the expected percentage of fibres for that time interval remained. This is in agreement with the findings for the persistence of fibres on garments, where the presence of an over garment has been demonstrated to result in a more rapid loss of fibres [14]. Overall, these persistence results appear within the range reported for non-smooth garments [10,20] and therefore the treatment of skin as a ‘smooth garment’ may be over-simplistic. Human skin also appears to differ from human hair, which retains fibres for longer than garments [19]. 4.2. Differential shedding The label inside the blue hooded top stated that the garment was composed of 80% cotton and 20% polyester. The generic class of approximately half of the initially transferred blue target fibres (2801), and all of the fibres recovered at t = 2 (268) and t = 5 h (176) was determined. The cotton/polyester ratios were found to be 69:31, 72:28 and 75:25 respectively. The results showed a modest and increasing bias towards cotton being retained at each stage. The greater loss of polyester fibres may be due to the smooth nature of polyester [14], with the convoluted structure of cotton producing a more tenacious contact between fibre and skin, and possibly between fibre and arm hair. These findings are in accordance with previous work [16] demonstrating that fibres shed from blended fabrics are not transferred in the proportions of manufacture.
Fig. 4. The length distribution of fibres transferred from the pink jumper at t = 0 and t = 5 h.
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Fig. 5. Distribution of background fibres according to perceived colour under reflected light (n = 12,399).
the 46 pink target fibres recovered after 5 h. For the blue garment, after 5 h, the size grouping with the highest frequency was still 1.1–2.0 mm, but the distribution had changed such that shorter fibres were more highly represented than longer fibres. The same overall trend was recorded for the pink wool garment, but with a more dramatic shift towards shorter lengths after 5 h, and the 0.5 mm size group having the highest frequency after 5 h. No pink wool fibres with length N6 mm were recorded after 5 h. The frequency of fibres in the final size grouping of N10 mm is misleading in both histograms as this group size is much larger than the others. Some disagreement exists in the literature over the effect of fibre length on persistence, with one study claiming that size distribution remains constant [10], and another reporting a confused picture with no clear trends [19]. The results above are in agreement with the studies by Krauss [12] and Robertson [14] which concluded that longer fibres are lost more quickly. This is thought to be because long fibres are more likely to suffer disturbance than short fibres [1].
4.3. Transfer and persistence (24 h)
4.5. Fibre population study
For the blue hooded top, 24 h persistence experiments were undertaken for 10 subjects. No fibres matching the target garments were recovered. For the pink jumper, 24 h persistence experiments were undertaken for 8 subjects and again, no matching fibres were found. Vigorous activity has been shown to modify the persistence of fibres [19], therefore the activity undertaken during the 24 h period was recorded for each subject. Although subject activity was found to vary, from sports to sedentary activities, no matching fibres were recovered and therefore any correlation with activity cannot be inferred from the results. The lack of matching fibres after 24 h is most likely due to the fact that all of the subjects showered or bathed during this time, as in the case of head hair, washing has previously been shown to remove the vast majority of fibres [19,11]. The waterproof nature of skin is undoubtedly a factor relating to this observation. In view of these results, experiments relating to a 48 h period were terminated.
The average numbers of coloured fibres recovered from the bare skin of subjects were 241 ± 143 fibres for women, and 458 ± 246 fibres for men. This difference was significant at the 5% level. As noted for the transfer of target fibres, greater numbers of background fibres were found on both hirsute subjects and those with a larger arm surface area.
4.4. Length The lengths of the 4038 blue target fibres and the 2470 pink target fibres initially transferred to subjects were estimated and their distributions are shown in Figs. 3 and 4. For both garments the size grouping with the highest frequency initially was 1.1–2.0 mm, but the distributions were different with only a small proportion of the pink target fibres having length N3.0 mm. The histograms also show the lengths of the 343 blue target fibres and
Fig. 6. Distribution of background fibres according to perceived colour under transmitted light (n = 491).
4.5.1. Colour 12,399 fibres taken from 21 subjects were classified according to perceived colour under reflected light (Fig. 5). Black/grey fibres made up almost three-quarters of the fibres classified (72.3%) followed by blue (12.4%), red (6.3%) brown (4.4%) and green (3.8%). The remaining colour groups made up less than 1% of the total, and consisted of pink/purple (0.8%) and 'other' (including yellow, ‘tiger tail’ and multi-coloured fibres) making up only 0.03%. Direct comparison with some previous population studies shows that the dominance of black fibres, followed by blue and red was also observed for fibres in head hair [7], on car seats [4] and in washing machines [6]. The four remaining minor colours do not always agree between published studies, probably because they will be heavily influenced by climate, season [7], and fashion. Direct comparison is not possible with all previously published population studies because the full colour results are not always reported [9]. For population studies using cinema seats [8] and white t-shirts [21], only the two most popular colours, (black and blue) were given, although this ranking agrees with the results of this study. In addition, direct comparisons cannot be made where population studies include colourless fibres [6]. Although not outside of the range previously reported, the number of green fibres reported in this study is likely to
Fig. 7. The distribution of background fibres according to length (n = 491).
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0.5 mm, 4% of the fibres fell into the 3.1–5.0 mm size grouping, and only 1% of fibres had length N5.0 mm. It is important to note that the size groupings are unequal in Fig. 7. Although the absolute percentages vary between studies, comparison with previous population studies on human head hair [7], car seats [4] and washing machines [2] shows agreement with the length rankings reported here (although fibres with length b0.5 mm were not included in the washing machine study). The length results do not agree with the population of fibres on outdoor surfaces which showed higher percentages of shorter fibres [9]. However, the authors of that particular study suggested that the fibres had become short as a result of damage over some time, and were not necessarily representative of recent transfer.
Fig. 8. Distribution of background fibres according to generic type (n = 491).
have been skewed by one set of background tapings which contained 145 green fibres out of 282 (51%). With the majority (if not all) fibre population studies, it is important to note that the perceived colour of the fibres is determined under reflected light. When fibres are viewed under transmitted light during comparison microscopy, the perceived colour is very often completely different to that perceived by the naked eye. The ‘corrected’ colour distribution for a sub-sample of 491 fibres Section 4.5.2 subsequently viewed under transmitted light microscopy is shown in Fig. 6. When compared to Fig. 5 it can be seen that the percentage of black/grey fibres has reduced from 73% to 50% with a corresponding increase in the other colours. When the corrected values are compared to those from previous population studies closer agreement between the values is obtained. The effect was most noticeable for black/grey fibres which were often observed to be dyed very dark blue or brown. 4.5.2. Length Of the 12,399 fibres classified according to perceived colour, 491 fibres were randomly selected according to the method described for the sampling of fibres recovered from head hair [7], and classified according to length (Fig. 7). The size grouping with the highest frequency in this sub-sample was 1.1–3.0 mm (with a frequency of 43%), followed by the size grouping 0.5–1.0 mm (27%). A quarter of the fibres had a length N
4.5.3. Fibre type Fig. 8 shows the sub-sample of 491 fibres classified according to generic fibre type. Analysis of the data showed that 80% of the fibres were natural and 20% were man-made. This is in agreement with previous population studies which have all reported a higher percentage of natural fibres. Within each of the natural and man-made classes the fibres were further sub-divided. The largest group of natural fibres was cotton (72%) followed by wool (8%). Polyester accounted for the highest proportion of man-made fibres (15%) followed by regenerated cellulosic and acrylic fibres (2%). Most of the ‘other’ group (2%) consisted of man-made fibres which were too darkly dyed or pigmented to be identified at this level of analysis. Comparison with the previously published population studies shows that cotton fibres have consistently been found to be the most abundant fibre type. This is perhaps unsurprising given that a clothing database compiled in Germany showed that 74% of summer clothing in the database was composed of cotton fibres [22]. Polyester was found to be the second most common fibre type in this study, which is also in agreement with the clothing database which found 15% of summer clothing to be composed of polyester fibres [22]. The proportion of polyester fibres also agrees with the population of fibres in head hair [7], but not with any other published population study. Discrepancies in the percentages and the order among the lesscommon fibre types can generally be accounted for by climatic differences in the region of study and the difference in sample sizes between the studies. As with colour, it is important to emphasise the ‘generic’ nature of this aspect of population studies. Since FTIR analysis has not been carried out on the man-made elements, the frequencies obtained are extremely conservative—particularly for polyamides and polyacrylonitriles.
Fig. 9. Distribution of fibres according to combined colour and generic class (n = 491).
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4.5.4. Fibre type/colour combination The sub-sample of 491 fibres was also classified according to both colour and generic class combination (Fig. 9). Cotton dominates the population with the two most prevalent combinations of black/grey cotton and blue cotton accounting for over half (56%). The fibre population studies of head hair [7], cinema seats [8], washing machines [2], car seats [4] and white t-shirts [21] all support the finding that black/grey cotton is the most popular colour/class combination followed by blue cotton. However, this study does not agree with a population study of Polish bus seats which found both blue cotton and green cotton to be more popular than black/grey cotton [6]. The third most common grouping in this study was black/ grey polyester, a position not supported by previous studies which have reported either red cotton [2,7] or black/grey wool [4,8] in this position. The next most common fibre class/colour combinations were blue wool (6%) and red cotton (5%) followed by green cotton, blue polyester and brown cotton (4%), brown polyester (3%) and black wool (2%). The remaining 16 groups had populations of 1% or smaller and in total accounted for less than 10% of the population. 4.5.5. Delustrant More than half of the man-made fibres observed in the sub-sample of 491 fibres were delustered (59%) which is higher than the values reported previously for the population of fibres on car seats (46%) [4]. There is little information about the relative percentages of delustered/non-delustered fibres within the various generic classes, but it has been suggested that non-delustered polyester fibres are in a minority [5]. 5. Conclusions While no general study can hope to provide insight or answers to every potential case, the results of the transfer and persistence aspect of this study can be used to assist in the forming of expectations of the number of fibres expected to remain on skin after a given time interval. Both target garments were chosen because of their high sheddability (particularly the brushed surface of the blue top) and a prolonged and forceful simulated contact was used to transfer the target fibres. These factors were designed to produce results representative of an upper limit or ‘best case’ scenario for the transfer and persistence of fibres on bare skin. It is therefore probable that the results obtained will be somewhat conservative in the majority of casework situations. The results therefore show that where significant numbers of fibres are found on the naked body of homicide victim, this would be incongruous with any assertion that contact took place with the source item over 24 h earlier—particularly if the victim was known to have bathed or showered within that time period and/or changed their clothes. The size distribution of the transferred fibres may also be an indicative factor. The results of the fibre population aspect of this study were generally in accordance with those previously published for other
substrates and can be used to complement the transfer and persistence data in the evaluating the significance of fibres recovered from bare skin found to match a questioned item. The comparison of the results of perceived colour under transmitted and reflected light, illustrates the generic nature of population studies and the extremely conservative results obtained. The results show that significant numbers of fibres can be expected to be recovered from skin and the difficulty faced in the intelligence phase of an investigation in determining what (if any) collectives present are foreign to the environment of the individual concerned— particularly when the clothing in question is absent. References [1] C.A. Pounds, K.W. Smalldon, The transfer of fibres between clothing materials during simulated contacts and their persistence during wear: Part III — a preliminary investigation of the mechanisms involved, J. Forensic Sci. Soc. 15 (3) (1975) 197–207. [2] R. Watt, C. Roux, J. Robertson, The population of coloured textile fibres in domestic washing machines, Sci. Justice 45 (2) (2005) 75–83. [3] R. Cook, M.T. Webb-Salter, L. Marshall, The significance of fibres found in head hair, Forensic Sci. Int. 87 (2) (1997) 155–160. [4] C. Roux, P. Margot, The population of textile fibres on car seats, Sci. Justice 37 (1) (1997) 25–30. [5] M.C. Grieve, A survey on the evidential value of fibres and on the interpretation of the findings in fibre transfer cases. Part 1 — fibre frequencies, Sci. Justice 40 (3) (2000) 189–200. [6] J. Was-Gubała, A. Chochoł, A population study of fibres found on bus seats in Cracow, Probl. Forensic Sci. 46 (2001) 249–254. [7] R. Palmer, S. Oliver, The population of coloured fibres in human head hair, Sci. Justice 44 (2) (2004) 83–88. [8] S. Cantrell, C. Roux, P. Maynard, J. Robertson, A textile fibre survey as an aid to the interpretation of fibre evidence in the Sydney region, Forensic Sci. Int. 123 (1) (2001) 48–53. [9] M.C. Grieve, T. Biermann, The population of coloured textile fibres on outdoor surfaces, Sci. Justice 37 (4) (1997) 231–239. [10] C.A. Pounds, K.W. Smalldon, The transfer of fibres between clothing materials during simulated contacts and their persistence during wear: Part II – fibre persistence, J. Forensic Sci. Soc. 15 (1) (1975) 29–37. [11] C.M. Ashcroft, S. Evans, I.R. Tebbett, The persistence of fibres in head hair, J. Forensic Sci. Soc. 28 (5–6) (1988) 289–293. [12] W. Krauss, Fibre persistence on garments under open-air conditions, Proceedings of European Fibres Group Meeting, Sweden, Linkoping, 1995, pp. 32–36. [13] C.B.M. Kidd, J. Robertson, The transfer of textile fibres during simulated contacts, J. Forensic Sci. Soc. 22 (3) (1982) 301–308. [14] J. Robertson, C.B.M. Kidd, H.M.P. Parkinson, The persistence of textile fibres transferred during simulated contacts, J. Forensic Sci. Soc. 22 (4) (1982) 353–360. [15] R. Palmer, M. Banks, The secondary transfer of fibres from head hair, Sci. Justice 45 (3) (2005) 123–128. [16] M.T. Salter, R. Cook, A.R. Jackson, Differential shedding from blended fabrics, Forensic Sci. Int. 33 (3) (1987) 155–164. [17] A.K. Davidson, L. Riley, Fibre recovery from wet and bloodstained surfaces. [18] W. Krauss, U. Hildebrand, Fibre persistence on skin under open-air conditions, Forensic Examination of Trace Evidence in Transition, 1996, p. 12, San Antonio, Texas, USA. [19] M.T. Salter, R. Cook, Transfer of fibres to head hair, their persistence and retrieval, Forensic Sci. Int. 81 (2–3) (1996) 211–221. [20] C.A. Pounds, The recovery of fibres from the surface of clothing for forensic examinations, J. Forensic Sci. Soc. 15 (2) (1975) 127–132. [21] G. Massonnet, M. Schiesser, C. Champod, Population of textile fibres on white t-shirts, Proceedings of The European Fibres Group Meeting, Dundee, 1998, pp. 76–80. [22] T.W. Biermann, M.C. Grieve, A computerized data base of mail order garments: a contribution toward estimating the frequency of fibre types found in clothing. Part 2: the content of the data bank and its statistical evaluation, Forensic Sci. Int. 77 (1–2) (1996) 75–91. [23] J.M. Miller, J.C. Miller, Statistics and Chemometrics for Analytical Chemistry, 5th ed., Pearson, 2005.
Contents lists available at ScienceDirect
Science and Justice j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s c i j u s
The population, transfer and persistence of fibres on the skin of living subjects Ray Palmer a,⁎, Hilary J. Burch a,b,1 a b
The Forensic Science Service, Hinchingbrooke Park, Huntingdon, Cambridgeshire, PE296NU, UK Centre for Forensic Science, University of Strathclyde, Royal College, 204 George St, Glasgow, G1 1XW, UK
a r t i c l e
i n f o
Article history: Received 19 January 2009 Received in revised form 25 February 2009 Accepted 28 February 2009 Keywords: Fibres Persistence Transfer Length Skin Bathing
a b s t r a c t Fibres were transferred to the bare arms of living subjects and their persistence determined at intervals up to 24 h, during which normal daily activity was undertaken. Decay curves showed an initial rapid loss followed by an apparently exponential decay. No target fibres were found to remain after 24 h. The length distribution showed a shift towards shorter fibre lengths and the differential shedding results for a polyester/cotton mixture showed a small bias towards the retention of cotton. The population of coloured fibres on bare skin was classified according to perceived colour, length, generic class and the presence or absence of delustrant. © 2009 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction The transfer and persistence of fibres have been the subject of a number of studies and the characteristics determined for a variety of substrates [1,3,10–15,19]. The data from these studies can be helpful in formulating expectations and evaluating the findings relating to specific casework scenarios where a time-frame for contact between a victim and their assailant needs to be estimated. In many homicides, it is not uncommon for the naked body of the victim to be deposited away from the original crime scene and for trace evidence such as fibres, potentially relating to the perpetrator, to be recovered from the skin of the victim. Using pig skin as a human analogue, Krauss and Hildebrand [18] studied the persistence characteristics of fibres on skin left outdoors and exposed to the elements over time. These authors found that the number of persisting fibres depended upon on the prevailing weather conditions, such that when the combination of wind and precipitation was recorded, fibre loss increased dramatically. These experiments never showed a total loss of fibres, suggesting that due to the lack of post-transfer activity, the probability of finding fibres originating from the offender's clothing on the skin of a homicide victim, in such circumstances, is very high. A complimentary study [17] showed that even when skin is bloodstained or wet, fibres are still recoverable using tape lifts, although the efficiency of recovery is reduced.
There does however, appear to be little if any further data relating to this substrate and to the authors' knowledge, none exists relating to the transfer and persistence of fibres on the skin of live human subjects, despite the fact that this may be useful in estimating the time-frame of contact between a victim and questioned item in the above scenario. Likewise, numerous ‘background’ fibre population studies have been performed on a variety of substrates [2,4–6,7–9] which provide data useful in the assessment of the significance of matching fibres. Again, to the authors' knowledge, no such data exists relating to the skin of live human subjects, which would undoubtedly compliment any obtained from a transfer and persistence study of this substrate. 2. Aims The aims of this study were to: • Investigate the transfer and persistence of fibres on bare skin with respect to factors of fibre type, gender, differential shedding and length. • Classify the background population of fibres on bare skin, in terms of perceived colour, length, and generic type. 3. Experimental 3.1. Target fibres
⁎ Corresponding author. E-mail address: [email protected] (R. Palmer). 1 Present address: The Royal Society of Chemistry, Thomas Graham House, Cambridge, CB4 0WF, UK.
A bright-blue knitted hooded top (80% cotton, 20% polyester mixture), and a bright-pink knitted jumper (100% wool) were chosen as the target garments for the transfer and persistence experiments.
1355-0306/$ – see front matter © 2009 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.scijus.2009.02.008
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The bright colours of the garments were selected for ease of subsequent identification and counting of target fibres. Although both garments were knitted, the inside of the hooded top had a brushed texture and this surface was used for transfer experiments due to its high transfer potential. Bulk samples of fibres from each garment were mounted and examined by high power brightfield and polarised light microscopy to confirm the fibre types listed on the garment labels, as well as providing controls for comparisons with problematic target fibres. 3.2. Fibre recovery Fibre recovery was achieved by pressing high-adhesive tape (J-LAR, 72 N/25 mm, 2 cm wide) onto the skin of the subjects. These tapings were then attached to transparent A5 acetate sheets which had been appropriately labelled [15]. The taping procedure was not reported to be uncomfortable by any of the subjects, in agreement with previous studies [7,19], although some arm hairs were removed, particularly from male subjects. Tapings were examined using a low power stereomicroscope (Nikon SMZ645) and target fibres were recorded by drawing circles on the acetate sheets using a permanent marker. 3.3. Transfer and persistence (0–5 h) Subjects were asked to attend wearing clothing that exposed their upper and lower arms. These areas of skin were taped to remove any background fibres (‘blanking’) and the tapes retained. Target fibres were transferred by contact between the skin and the target garment in question. The contact involved wrapping the sleeves of the garment around the arms of the subject (see Fig. 1) and moving the sleeves along the length of each arm and over the hands. The simulated contact was standardised as far as possible for all subjects, and was intended to represent a prolonged and forceful contact. The subject's skin was then taped immediately and the number of target fibres counted to establish an initial (t = 0) value. Subjects were subjected to the transfer procedure again and asked to return after a designated time interval (from 0.5 to 5 h). Subjects were asked not to cover their skin during this time interval, as it has been shown previously that the presence of an over garment results in a more rapid loss of fibres [14]. After the designated time period had elapsed, the subjects were taped again and the number of remaining target fibres counted. A note was made of the colour and fibre content of the upper garments worn by each subject on each occasion, and a tape lift of the garment taken.
Fig. 2. Decay curves for fibres on bare skin for (a) the pink wool jumper and (b) the blue hooded top.
3.4. 24 h persistence experiments In an extension of the persistence study, target fibres were transferred to the subjects who were asked to return in 24 h. The subjects were instructed to carry out their normal activities, including bathing or showering (subjects were provided with a white cotton towel for use after bathing to speed up searching and minimise spurious blue cotton matches). Depending on the results from this aspect of the study a similar exercise was planned for a 48 h interval. Anti-contamination measures were taken during fibre recovery and included hand washing, wearing gloves and conducting the tapings in a room separate to that used for contact with, and storage of, the target garments. 3.5. Length The lengths of any recovered target fibres were estimated by comparison with a millimetre scale under a search microscope [9]. 3.6. Differential shedding The respective numbers of cotton and polyester fibres for the blue hooded top were recorded at t = 0, t = 2 h and t = 5 h. 3.7. Population study
Fig. 1. Method of fibre transfer.
The tape lifts used for the blanking process at the start of the transfer and persistence experiments were used to determine the population of coloured fibres on the bare skin of the subjects. The fibres were classified according to perceived colour (under both reflected and transmitted light), generic class, length and (in the case of man-made fibres) the presence or absence of delustrant. Fibre generic class was established using a combination of brightfield and (where appropriate),
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Fig. 3. The length distribution of the fibres transferred from the blue hooded top at t = 0 and t = 5 h.
polarised light microscopy using a Leitz Ortholux II POL-BK polarising microscope equipped with a 20-order tilting compensator to obtain birefringence values. 4. Results and discussion 4.1. Transfer and persistence (0–5 h) 48 persistence experiments were performed for the blue hooded top and 37 persistence experiments were performed for the pink wool jumper, involving intervals of 0.5, 1, 2, 3, 4 and 5 h for each garment. The decay curves for both garments are shown in Fig. 2. Both decay curves show one standard deviation limits for each time interval. 23 initial transfer experiments were performed for the blue hooded top, and the average number of blue fibres initially transferred was 245 ± 142 (range = 106–730). 21 initial transfer experiments were performed for the pink wool jumper, and the average number of pink fibres initially transferred was 133 ± 50 (range = 48–214). The difference between the initial transfer values for blue and pink garments was significant at the 5% level using standard t-testing [23]. As the same type of contact was used in both sets of experiments, these results can be attributed to the fact that the wool garment shedded less easily than the polyester/cotton garment. There was also variation within transfer experiments using the same garment by gender, with apparently fewer blue fibres being transferred to women. The difference in the number of pink fibres transferred to men and women was however, not significant at the 5% level. It is likely that the number of fibres transferred was mainly dependent on two variables; the arm surface area and the density of arm hair (the number of initially transferred fibres was consistently higher for hirsute subjects). The standard deviations are high for both garments, which is a result of several factors. Firstly, the high standard deviations reflect the variation in persistence between individuals found in this type of study. Variations in persistence are due to individual differences in skin surface texture (with more hirsute subjects being more retentive) and also variation in subject activity following the seeding [19]. Secondly, the high standard deviations reflect the inherent variability of initial primary transfer [15]. Although the simulated contact was standardised in all transfer experiments, it is impossible to produce exact duplicates in this type of study because of natural variations in the force applied during contact with the garment. It is also possible that the propensity of the garments to shed decreased with repeated use. The standard deviations are higher at the earlier time intervals because they reflect the larger experimental error when the rate of fibre loss is greatest [10]. When the rate of fibre loss is high, small timing errors are magnified.
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The overall shape of the decay curves in Fig. 2 appears exponential after an initial rapid loss. The difference in persistence between male and female subjects was not significant at the 5% level for either garment. After 5 h approximately 15% of the blue cotton and polyester fibres remained (see Differential shedding). The rate of loss of the pink wool fibres was higher however, with only 5% of fibres remaining after 5 h. The difference in rate of loss between blue and pink garments was significant at the 5% level [23]. In most of the previous persistence studies, no difference between the persistence of wool and other fibre types was reported [10,11,14,19], but the greater persistence of cotton fibres over wool fibres is not in agreement with results obtained for human head hair [15]. It has been suggested that woollen fibres might persist in human hair for longer than other fibre types, because of hair-to-hair interactions between both rough scaled surfaces [11,15]. This however, does not appear to be the case for human skin and may be related to the difference in hair morphology, density and surface area from head hair. During some persistence experiments, subjects were required to wear a lab coat as part of their normal daily activity (white 35% cotton and 65% polyester) over the areas of skin to which the fibres were transferred. When subjects were subsequently taped, only 20% of the expected percentage of fibres for that time interval remained. This is in agreement with the findings for the persistence of fibres on garments, where the presence of an over garment has been demonstrated to result in a more rapid loss of fibres [14]. Overall, these persistence results appear within the range reported for non-smooth garments [10,20] and therefore the treatment of skin as a ‘smooth garment’ may be over-simplistic. Human skin also appears to differ from human hair, which retains fibres for longer than garments [19]. 4.2. Differential shedding The label inside the blue hooded top stated that the garment was composed of 80% cotton and 20% polyester. The generic class of approximately half of the initially transferred blue target fibres (2801), and all of the fibres recovered at t = 2 (268) and t = 5 h (176) was determined. The cotton/polyester ratios were found to be 69:31, 72:28 and 75:25 respectively. The results showed a modest and increasing bias towards cotton being retained at each stage. The greater loss of polyester fibres may be due to the smooth nature of polyester [14], with the convoluted structure of cotton producing a more tenacious contact between fibre and skin, and possibly between fibre and arm hair. These findings are in accordance with previous work [16] demonstrating that fibres shed from blended fabrics are not transferred in the proportions of manufacture.
Fig. 4. The length distribution of fibres transferred from the pink jumper at t = 0 and t = 5 h.
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Fig. 5. Distribution of background fibres according to perceived colour under reflected light (n = 12,399).
the 46 pink target fibres recovered after 5 h. For the blue garment, after 5 h, the size grouping with the highest frequency was still 1.1–2.0 mm, but the distribution had changed such that shorter fibres were more highly represented than longer fibres. The same overall trend was recorded for the pink wool garment, but with a more dramatic shift towards shorter lengths after 5 h, and the 0.5 mm size group having the highest frequency after 5 h. No pink wool fibres with length N6 mm were recorded after 5 h. The frequency of fibres in the final size grouping of N10 mm is misleading in both histograms as this group size is much larger than the others. Some disagreement exists in the literature over the effect of fibre length on persistence, with one study claiming that size distribution remains constant [10], and another reporting a confused picture with no clear trends [19]. The results above are in agreement with the studies by Krauss [12] and Robertson [14] which concluded that longer fibres are lost more quickly. This is thought to be because long fibres are more likely to suffer disturbance than short fibres [1].
4.3. Transfer and persistence (24 h)
4.5. Fibre population study
For the blue hooded top, 24 h persistence experiments were undertaken for 10 subjects. No fibres matching the target garments were recovered. For the pink jumper, 24 h persistence experiments were undertaken for 8 subjects and again, no matching fibres were found. Vigorous activity has been shown to modify the persistence of fibres [19], therefore the activity undertaken during the 24 h period was recorded for each subject. Although subject activity was found to vary, from sports to sedentary activities, no matching fibres were recovered and therefore any correlation with activity cannot be inferred from the results. The lack of matching fibres after 24 h is most likely due to the fact that all of the subjects showered or bathed during this time, as in the case of head hair, washing has previously been shown to remove the vast majority of fibres [19,11]. The waterproof nature of skin is undoubtedly a factor relating to this observation. In view of these results, experiments relating to a 48 h period were terminated.
The average numbers of coloured fibres recovered from the bare skin of subjects were 241 ± 143 fibres for women, and 458 ± 246 fibres for men. This difference was significant at the 5% level. As noted for the transfer of target fibres, greater numbers of background fibres were found on both hirsute subjects and those with a larger arm surface area.
4.4. Length The lengths of the 4038 blue target fibres and the 2470 pink target fibres initially transferred to subjects were estimated and their distributions are shown in Figs. 3 and 4. For both garments the size grouping with the highest frequency initially was 1.1–2.0 mm, but the distributions were different with only a small proportion of the pink target fibres having length N3.0 mm. The histograms also show the lengths of the 343 blue target fibres and
Fig. 6. Distribution of background fibres according to perceived colour under transmitted light (n = 491).
4.5.1. Colour 12,399 fibres taken from 21 subjects were classified according to perceived colour under reflected light (Fig. 5). Black/grey fibres made up almost three-quarters of the fibres classified (72.3%) followed by blue (12.4%), red (6.3%) brown (4.4%) and green (3.8%). The remaining colour groups made up less than 1% of the total, and consisted of pink/purple (0.8%) and 'other' (including yellow, ‘tiger tail’ and multi-coloured fibres) making up only 0.03%. Direct comparison with some previous population studies shows that the dominance of black fibres, followed by blue and red was also observed for fibres in head hair [7], on car seats [4] and in washing machines [6]. The four remaining minor colours do not always agree between published studies, probably because they will be heavily influenced by climate, season [7], and fashion. Direct comparison is not possible with all previously published population studies because the full colour results are not always reported [9]. For population studies using cinema seats [8] and white t-shirts [21], only the two most popular colours, (black and blue) were given, although this ranking agrees with the results of this study. In addition, direct comparisons cannot be made where population studies include colourless fibres [6]. Although not outside of the range previously reported, the number of green fibres reported in this study is likely to
Fig. 7. The distribution of background fibres according to length (n = 491).
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0.5 mm, 4% of the fibres fell into the 3.1–5.0 mm size grouping, and only 1% of fibres had length N5.0 mm. It is important to note that the size groupings are unequal in Fig. 7. Although the absolute percentages vary between studies, comparison with previous population studies on human head hair [7], car seats [4] and washing machines [2] shows agreement with the length rankings reported here (although fibres with length b0.5 mm were not included in the washing machine study). The length results do not agree with the population of fibres on outdoor surfaces which showed higher percentages of shorter fibres [9]. However, the authors of that particular study suggested that the fibres had become short as a result of damage over some time, and were not necessarily representative of recent transfer.
Fig. 8. Distribution of background fibres according to generic type (n = 491).
have been skewed by one set of background tapings which contained 145 green fibres out of 282 (51%). With the majority (if not all) fibre population studies, it is important to note that the perceived colour of the fibres is determined under reflected light. When fibres are viewed under transmitted light during comparison microscopy, the perceived colour is very often completely different to that perceived by the naked eye. The ‘corrected’ colour distribution for a sub-sample of 491 fibres Section 4.5.2 subsequently viewed under transmitted light microscopy is shown in Fig. 6. When compared to Fig. 5 it can be seen that the percentage of black/grey fibres has reduced from 73% to 50% with a corresponding increase in the other colours. When the corrected values are compared to those from previous population studies closer agreement between the values is obtained. The effect was most noticeable for black/grey fibres which were often observed to be dyed very dark blue or brown. 4.5.2. Length Of the 12,399 fibres classified according to perceived colour, 491 fibres were randomly selected according to the method described for the sampling of fibres recovered from head hair [7], and classified according to length (Fig. 7). The size grouping with the highest frequency in this sub-sample was 1.1–3.0 mm (with a frequency of 43%), followed by the size grouping 0.5–1.0 mm (27%). A quarter of the fibres had a length N
4.5.3. Fibre type Fig. 8 shows the sub-sample of 491 fibres classified according to generic fibre type. Analysis of the data showed that 80% of the fibres were natural and 20% were man-made. This is in agreement with previous population studies which have all reported a higher percentage of natural fibres. Within each of the natural and man-made classes the fibres were further sub-divided. The largest group of natural fibres was cotton (72%) followed by wool (8%). Polyester accounted for the highest proportion of man-made fibres (15%) followed by regenerated cellulosic and acrylic fibres (2%). Most of the ‘other’ group (2%) consisted of man-made fibres which were too darkly dyed or pigmented to be identified at this level of analysis. Comparison with the previously published population studies shows that cotton fibres have consistently been found to be the most abundant fibre type. This is perhaps unsurprising given that a clothing database compiled in Germany showed that 74% of summer clothing in the database was composed of cotton fibres [22]. Polyester was found to be the second most common fibre type in this study, which is also in agreement with the clothing database which found 15% of summer clothing to be composed of polyester fibres [22]. The proportion of polyester fibres also agrees with the population of fibres in head hair [7], but not with any other published population study. Discrepancies in the percentages and the order among the lesscommon fibre types can generally be accounted for by climatic differences in the region of study and the difference in sample sizes between the studies. As with colour, it is important to emphasise the ‘generic’ nature of this aspect of population studies. Since FTIR analysis has not been carried out on the man-made elements, the frequencies obtained are extremely conservative—particularly for polyamides and polyacrylonitriles.
Fig. 9. Distribution of fibres according to combined colour and generic class (n = 491).
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4.5.4. Fibre type/colour combination The sub-sample of 491 fibres was also classified according to both colour and generic class combination (Fig. 9). Cotton dominates the population with the two most prevalent combinations of black/grey cotton and blue cotton accounting for over half (56%). The fibre population studies of head hair [7], cinema seats [8], washing machines [2], car seats [4] and white t-shirts [21] all support the finding that black/grey cotton is the most popular colour/class combination followed by blue cotton. However, this study does not agree with a population study of Polish bus seats which found both blue cotton and green cotton to be more popular than black/grey cotton [6]. The third most common grouping in this study was black/ grey polyester, a position not supported by previous studies which have reported either red cotton [2,7] or black/grey wool [4,8] in this position. The next most common fibre class/colour combinations were blue wool (6%) and red cotton (5%) followed by green cotton, blue polyester and brown cotton (4%), brown polyester (3%) and black wool (2%). The remaining 16 groups had populations of 1% or smaller and in total accounted for less than 10% of the population. 4.5.5. Delustrant More than half of the man-made fibres observed in the sub-sample of 491 fibres were delustered (59%) which is higher than the values reported previously for the population of fibres on car seats (46%) [4]. There is little information about the relative percentages of delustered/non-delustered fibres within the various generic classes, but it has been suggested that non-delustered polyester fibres are in a minority [5]. 5. Conclusions While no general study can hope to provide insight or answers to every potential case, the results of the transfer and persistence aspect of this study can be used to assist in the forming of expectations of the number of fibres expected to remain on skin after a given time interval. Both target garments were chosen because of their high sheddability (particularly the brushed surface of the blue top) and a prolonged and forceful simulated contact was used to transfer the target fibres. These factors were designed to produce results representative of an upper limit or ‘best case’ scenario for the transfer and persistence of fibres on bare skin. It is therefore probable that the results obtained will be somewhat conservative in the majority of casework situations. The results therefore show that where significant numbers of fibres are found on the naked body of homicide victim, this would be incongruous with any assertion that contact took place with the source item over 24 h earlier—particularly if the victim was known to have bathed or showered within that time period and/or changed their clothes. The size distribution of the transferred fibres may also be an indicative factor. The results of the fibre population aspect of this study were generally in accordance with those previously published for other
substrates and can be used to complement the transfer and persistence data in the evaluating the significance of fibres recovered from bare skin found to match a questioned item. The comparison of the results of perceived colour under transmitted and reflected light, illustrates the generic nature of population studies and the extremely conservative results obtained. The results show that significant numbers of fibres can be expected to be recovered from skin and the difficulty faced in the intelligence phase of an investigation in determining what (if any) collectives present are foreign to the environment of the individual concerned— particularly when the clothing in question is absent. References [1] C.A. Pounds, K.W. Smalldon, The transfer of fibres between clothing materials during simulated contacts and their persistence during wear: Part III — a preliminary investigation of the mechanisms involved, J. Forensic Sci. Soc. 15 (3) (1975) 197–207. [2] R. Watt, C. Roux, J. Robertson, The population of coloured textile fibres in domestic washing machines, Sci. Justice 45 (2) (2005) 75–83. [3] R. Cook, M.T. Webb-Salter, L. Marshall, The significance of fibres found in head hair, Forensic Sci. Int. 87 (2) (1997) 155–160. [4] C. Roux, P. Margot, The population of textile fibres on car seats, Sci. Justice 37 (1) (1997) 25–30. [5] M.C. Grieve, A survey on the evidential value of fibres and on the interpretation of the findings in fibre transfer cases. Part 1 — fibre frequencies, Sci. Justice 40 (3) (2000) 189–200. [6] J. Was-Gubała, A. Chochoł, A population study of fibres found on bus seats in Cracow, Probl. Forensic Sci. 46 (2001) 249–254. [7] R. Palmer, S. Oliver, The population of coloured fibres in human head hair, Sci. Justice 44 (2) (2004) 83–88. [8] S. Cantrell, C. Roux, P. Maynard, J. Robertson, A textile fibre survey as an aid to the interpretation of fibre evidence in the Sydney region, Forensic Sci. Int. 123 (1) (2001) 48–53. [9] M.C. Grieve, T. Biermann, The population of coloured textile fibres on outdoor surfaces, Sci. Justice 37 (4) (1997) 231–239. [10] C.A. Pounds, K.W. Smalldon, The transfer of fibres between clothing materials during simulated contacts and their persistence during wear: Part II – fibre persistence, J. Forensic Sci. Soc. 15 (1) (1975) 29–37. [11] C.M. Ashcroft, S. Evans, I.R. Tebbett, The persistence of fibres in head hair, J. Forensic Sci. Soc. 28 (5–6) (1988) 289–293. [12] W. Krauss, Fibre persistence on garments under open-air conditions, Proceedings of European Fibres Group Meeting, Sweden, Linkoping, 1995, pp. 32–36. [13] C.B.M. Kidd, J. Robertson, The transfer of textile fibres during simulated contacts, J. Forensic Sci. Soc. 22 (3) (1982) 301–308. [14] J. Robertson, C.B.M. Kidd, H.M.P. Parkinson, The persistence of textile fibres transferred during simulated contacts, J. Forensic Sci. Soc. 22 (4) (1982) 353–360. [15] R. Palmer, M. Banks, The secondary transfer of fibres from head hair, Sci. Justice 45 (3) (2005) 123–128. [16] M.T. Salter, R. Cook, A.R. Jackson, Differential shedding from blended fabrics, Forensic Sci. Int. 33 (3) (1987) 155–164. [17] A.K. Davidson, L. Riley, Fibre recovery from wet and bloodstained surfaces. [18] W. Krauss, U. Hildebrand, Fibre persistence on skin under open-air conditions, Forensic Examination of Trace Evidence in Transition, 1996, p. 12, San Antonio, Texas, USA. [19] M.T. Salter, R. Cook, Transfer of fibres to head hair, their persistence and retrieval, Forensic Sci. Int. 81 (2–3) (1996) 211–221. [20] C.A. Pounds, The recovery of fibres from the surface of clothing for forensic examinations, J. Forensic Sci. Soc. 15 (2) (1975) 127–132. [21] G. Massonnet, M. Schiesser, C. Champod, Population of textile fibres on white t-shirts, Proceedings of The European Fibres Group Meeting, Dundee, 1998, pp. 76–80. [22] T.W. Biermann, M.C. Grieve, A computerized data base of mail order garments: a contribution toward estimating the frequency of fibre types found in clothing. Part 2: the content of the data bank and its statistical evaluation, Forensic Sci. Int. 77 (1–2) (1996) 75–91. [23] J.M. Miller, J.C. Miller, Statistics and Chemometrics for Analytical Chemistry, 5th ed., Pearson, 2005.