Glass Practical - Essay Example

Glass evidence in Forensic science 1.0 Introduction During the glass breaking incidents viz. Burglary, hit and run accidents etc., minute glass fragments can be transferred onto the hair, clothing and footwear of people. The number of fragments transferred decreases rapidly with distance from the breaking pane. Aside from backscatter i. e. showering of glass pieces towards the striker', pieces can also be acquired, for example, by climbing through a broken window or walking over the broken glass (Benchmark, 2009). To begin with forensic examination, glass fragments can be observed under microscope. Refractive Index (RI) determination is a simple test to trace glass pieces to reference glass source; it associates breakers to the alleged crime. The present experiment is based on detection of glass particles present on garments of different weave. 2.0 Review of Literature 2.1 Glass fragments on garments: Curran et al (2000, p10) reported that transfer of glass occurs when a window is broken. As a result of the strike, backward fragmentation or backscatter of the glass pieces would be deposited on persons a few feet from the site. Persons present at 1.5 or even up to 3 m in the vicinity of the incident may have glass pieces into their garments (Benchmark) The size of fragments found depends on type of glass. Large pieces of glass are found in cases of hit and run accidents (collision of vehicles) and ram raids (forced entry). The glass fragments transferred on clothing are small pieces 0.1 to 2 mm in irregular shape. Curran et al. (2000, p115) reported a number of studies, those showing experimental (deliberate) deposition of glass pieces into clothing as well as creating criminal breaking conditions,. In an experiment, the glass pieces of 0.1 mm to 0.5 mm and 0.5 mm to 1 mm were put on the woolen sweater, tweed and sports jackets. It was observed that glass pieces are lost from clothing very fast specially those larger than 0.5 mm. The woolen sweater in this experiment retained only 8% of glass pieces after 6 hrs. The results of next experiment differed somewhat from the earlier one. Glass pieces were deposited on cotton (denim) and wool/acrylic (70:30) using an air rifle. Thereafter, the retention of these was examined under microscope between 30 min. to 6h. It was surprising that glass pieces between 1 to 0.5 mm were found on clothing but less than 0.5 mm were not retained. It may be because a critical size is necessary for retention or the small pieces could not be detected by microscope. Glass was also retained longer on denim than on wool/acrylic in this case. They also reported results of actual window breaking conditions created in the laboratory also. The window panes were broken by hammer till all glass was removed from the frame. The clothing of person present around showed 2-100 pieces after 1 h. 2.2 Persistence of glass fragments onto clothing of general public: Curran et al (2000: 88) emphasized that it is necessary to observe data on presence of glass fragments on clothing of general population prior to linking a suspect with breaking crime. Hoefler et al (In Curran et al., 2000) examined outer surface of clothing sampled randomly and found 41% of the total samples had no glass fragments, 53. 8% with 1-8 pieces of glass while 5.2% had more than 10 fragments. The majority of fragments recovered were 0.1 mm. Lau et al (as in Curran, 2000) studied student population’s clothing for glass fragments. The frequency of getting glass pieces in their experiment was, in every 6 garments 5 had one piece each while the sixth garment had 2 glass fragments. The fragments were smaller than 1 mm. The limitation of this study is that it was conducted on a specific group of persons and clothing e. g. T-shirts. Pearson et al examined 100 suits submitted to a dry cleaner. Of these, glass fragments were found on 63 suits. Total 551 fragments were found in their experiment and 253 of these were present on just two of these suits. The majority of pieces were 0.5-0.1 mm. If the recovered glass does not form a group of fragment than it is not due to crime as can be revealed by RI measurements. As later work on same experiment revealed. 2.3 Forensic interpretation of glass pieces onto garments: Lambert et al (as in Caddy, 117) examined criminal suspect for glass fragments. Of the 589 suspect only 12% had presence of glass fragments in descending order as shoes>trousers>jacket>knitwear>shirt. This sample was however from suspects, expected to have committed crime. Hicks et al (1996) provided important points for forensic interpretations based on their experiment. According to them the number of fragments recovered would depend on: Number of strikes: important but not much related to the tool used to break the glass. Striking the pane several times: leads to many more particles (72 to 127) and the glass pieces were mostly transferred onto upper garments. The result could well be used to determine height of strike relative to the height of breaker (Luce as cited in Hicks et al., 1996). Distance between glass and person: clear relationship between number of glass pieces on clothing and person breaking it or someone standing nearby Size of glass fragments: most of the glass was lost in first half hour of breaking. While smaller fragment retained longer than larger ones. After 8 hours of the breaking incidents, the glass fragments found into the breaker’s garment were in the size range 0.2-0.5 mm compared to immediately after transfer when 20% of the fragments were larger than 0.5 mm. Composition and weave of garment: glass was retained better by coarsely woven rather than into tightly woven fabrics. The composition and weave of the garments not only affected the retention of glass pieces but also the size of these pieces retained. The coarse clothing material viz. woolen pullover retained longer and the bigger pieces of glass. The smooth cotton top did not retain any pieces bigger than 0.2 mm after 8 h. but the woolen pullover retained 10% of the bigger glass pieces after the same time. The weave and material of clothing is important as the friction provided by the material would certainly affect retention of glass pieces on it. Benchmark found the activity of the breaker and texture of material of his garment affect retention of glass pieces, a woolen jumper is likely to retain glass pieces much longer than a smooth material e, g. leather, and polyester. Fragments may trap in sutures, pockets and cuffs of the garments. Time interval between breaking and subsequent recovery of glass from clothing: The number of fragments recovered is much less important than the association of recovered glass to incident. Because the former only means the effort made to recover glass from the garment, it does not tell anything about the number of fragments present at time zero. Curran et al (as in Caddy, 1996) added more points to Hicks et al’s observation, these are: Type and thickness of glass: Larger pieces may be found in case the glass is thicker The size of window: Larger the window more would be glass in it and so the pieces on the breakers garments. Weather at that time: Humid weather may cause more fragments to persist Whether the person entered the premises or not: If the person entered through the broken glass, he would be having more pieces besides the typical glass cuts on his cloths. Whether the clothing was confiscated with force: Force may make a number of pieces to dislodge from the garment Efficiency of laboratory method: Efficiency of methods used to detect glass pieces. Suitable methods are required to detect glass as the color of garment may make detection difficult. 3.0 Methodology: In the current experiment the presence of glass pieces was detected on garments collected by four investigators. The details of these samples are presented in Table-1 Table. 1 Samples collected by Details of samples No. of glass pieces found TARYN HEATHER SCOTT ME 1- Grey stripped vest top. 54% cotton 40% polyester 3% polyamide fiber 2- Grey wooly polo neck top. 38% polyester 3% Alsatian 3-Green long sleeve top 100% cotton 1- Purple cardie pockets 75% payester 25% cotton 2- Purple jumper 100% cotton 3- Black vest top 95% cotton 5% elastane 1- jersey T-shirt 100% nylon 2- Adidas T-shirt 100% polyester 3- underormour 63% nylon 23% polyester 14% elastine 1- Yellow T-shirt 100% cotton 2- blue T-shirt 100% cotton 3- Yellow T-shirt 100% cotton NO GLASS TWO PIECES OF GLASSES NO GLASS NO GLASS NO GLASS NO GLASS 3 PIECES OF GLASSES ONE PIECE OF GLASS ONE PIECE OF GLASSES NO GLASS NO GLASS NO GLASS Interpretation: The experiment is about retention of glass fragments on different types of fabrics. All the samples brought by Scott show presence of 1-3 glass pieces. Though the number of pieces found is small, to the level found in general public yet samples are tightly woven synthetic cloth which is not very good in retaining glass pieces so at least there is a hint of wearer’s association with some kind of glass breaking. As stated (Benchmark, 2009) though a surer indication is presence of numerous glass pieces soon after the breaking incident in which more than one type of matching glass is found, while one or two pieces of glass on a garment taken after many days of the incident may also relate alleged suspect with the crime. Besides sample number 2. by Taryn shows one glass piece. Since wool is known to retain glass pieces on account of its coarse texture, it is within the limits found in general population. The experiment also requires to look at the efficiency of detection since the color of cloth may have caused many pieces go undetected. The following information is also required to come to a conclusion of forensic importance: Size of the glass pieces Comparison of pieces with reference glass Time elapsed between incident and sampling since more pieces are found immediately while number decreases with passing time Sensitivity of detection method used. Whether the method detects small pieces and whether the color of garment interferes with detection. Conclusion: RI determination does show that how many time a reference glass is detected on a particular garment. Though it is not very useful information for forensic purposes as most of the glass breakage linked to criminal activities typically originates from broken window. However, since it is reported that glass found on clothing of general public is from containers viz. drinking glass or bottles, RI data are important It is to be noted here that buildings constructed at different times have used different types of glasses. So glass from a building can not be generalized for all others and using databases in such case require caution (Benchmark, 2009). Besides, number and distribution patterns of glass fragments on the clothing, whether more on upper or lower garments, are also necessary to correlate it with the crime. Incidents of glass pieces on garments generally found is also to be kept in mind The glass pieces may also be transferred between two persons when they come in contact with each other. For example sitting together in a car though only one or two fragments are likely to pass in this way. Though such a possibility bears any forensic importance is yet to be proved. Moreover, the possible transfer of glass between a person who has broken a window and a second person has been investigated by Allen et al. (as in Stoecklein & Becker, 1998 ). In these Experiments, the breaker sat next to a second person in the van. However, out of a total of 15 experimental runs only one fragment of glass was transferred to the garments of the second person. So persons with glass fragments on them can transfer to other persons coming in casual contact, but it is very small possibility and thus of little forensic importance (Stoecklein & Becker, 1998). So when one relating only a few glass pieces to crime, utmost care is necessary. REFERENCES Benchmark (2009) “Glass Analysis - "Seeing through glass", Forensic ACCESS, http://www.forensic access.co.uk/forensic-access-publications/benchmark-newsletter/glass-analysis.htm [ 28 Feb 2009] Caddy, B. (1996). Trace evidence analysis and interpretation: glass and paint, CRC Press Curran, J M, Hicks, T N &. Buckleton, J S (2000), Forensic Interpretation of Glass, CRC Press, 2000 Hicks, T, Vanina, R & Margot, P (1996) ‘Transfer and persistence of glass fragments on garments’, Science & Justice,vol.36, no. 2, pp 101-107. Stoecklein, W & Becker, S (1998) Paint and Glass: A Review’, In: 13th INTERPOL Forensic Science Symposium, Lyon, France, October 16-19 2001 http://www.interpol.int/public/Forensic/IFSS/meeting13/Reviews/PaintGlass.pdf [28 Feb 2009] Read More