Using of Glass Examination of Determining the Association of the Evidence with the Event - Research Proposal Example

PRACTICAL WRITE-UP ON GLASS EXAMINATION CONDUCTED BY FOUR STUDENTS INTRODUCTION Glass is a solid that has an amorphous structure. It is an inorganic product of fusion that has cooled to a rigid condition without crystallizing. Glass fragments is a hard, brittle, amorphous substance that is composed of silicon oxides mixed with various metal oxides. Amorphous solids have their atoms arranged randomly, unlike crystals. Tempered glass is stronger than normal glass due to rapid heating and cooling. Laminated glass found in car windshields has a layer of plastic between two pieces of ordinary window glass. During crime investigation, police may examine the clothing of the suspect to determine the presence of glass shards. The assumption is that if the suspect is near the car or building when the glass was broken, the suspect should be covered with glass fragments. If glass fragments are found, these should be analyzed. The number of glass fragments found on the suspect is important in establishing cases against a perpetrator. That is, the more shards found, the closer is the proximity of the perpetrator to the event. The examiner can determine what type of glass is found. For example, tempered glass is used in car side windows. The issue of glass comparison is one that depends on the need to find and measure those properties that will associate one glass fragment with another while minimizing or eliminating other sources. To compare glass fragments, a forensic scientist evaluates two important physical properties, the density and the refractive index. Flotation Method is an accurate and quick method for comparing glass densities. Using this method, a glass particle is immersed in a liquid. The density of that liquid is carefully adjusted through the addition of small amounts of an appropriate liquid until the glass chip remains suspended in the liquid medium. At this point, the glass will have the same density as the liquid medium and can be compared to other relevant pieces of glass which will remain suspended, sink, or float. Refractive Light Method Crystalline solids have definite geometric forms because of the orderly arrangement of their atoms. These solids refract a beam of light in two different light-ray components. This results in double refraction. REVIEW OF RELATED LITERATURE The Composition and Manufacture of Glass and its Domestic and Industrial Applications The two groups of glass are the oxide glass and non-oxide glass. The composition of oxide glasses include oxides. On the other hand, the composition of non-oxide glasses are compounds that contain no oxides and which often instead contain sulfides or metals. Oxide glasses are much more widely used commercially. Soda-lime glass is the kind of glass used for flat glass, most containers, electric light bulbs and other industrial and art objects. The composition is about seventy-two per cent (72%) silica, thirteen per cent (13%) sodium oxide, eleven percent (11%) calcium oxide and four percent (4%) minor ingredients.1 Soda-lead glass or crystal or lead glass, is made by substituting lead oxide for calcium oxide and often form part of the silica used in soda-lime glass. It has beautiful optical properties that it is widely used for the finest tableware and art objects. Likewise, lead oxide improves the electrical properties of glass.2 Borosilicate glass is heat-shock resistant. It contains about eighty percent (80%) silica, four percent (4%) sodium oxide, two percent (2%) alumina and thirteen percent (13) boric oxide. Such glass is about three times as heat-shock resistant as soda-lime glass and is excellent for chemical and electrical uses. This glass makes possible such products as ovenware and beakers, test tubes, and other laboratory equipment. Fused silica glass is a highly heat-shock resistant glass that consists entirely of silica. It can be heated to extremely high temperatures and then plunged into ice-cold water without cracking. Fused silica is expensive because exceptionally high temperatures must be maintained during production. It is used in laboratory glassware and optical fibers. Microscopic Techniques for Glass Examination The elemental composition of glass can be measured through the use of the scanning electron microscope. Another way is through x-ray fluorescence. Other methods of measurement is by flameless atomic absorption spectrophotometry. Still another is through inductively coupled plasma methods.3 Elemental Analysis of Glass Fragments Elemental analysis by solution ICP-MS of small amounts of glass can be done for the comparison between a fragment found at a crime scene to a possible source of the glass gives high accuracy. The multi-element capability and the sensitivity of ICP-MS combined with the simplified sample introduction of laser ablation prior to ion detection provides for an excellent and relatively non-destructive technique for elemental analysis of glass fragments. The direct solid sample introduction technique of laser ablation (LA) is reported as an alternative to the solution method.4 Statistical Interpretation of Glass Evidence Statistical interpretation of glass evidence can be used when examining a sample of glass fragments recovered from a suspect. The statistical analysis will give an idea if the suspect break the glass at the crime scene. The analysis will also determine if the glass fragments recovered from the suspect come from more than one source.5 Likewise, it will show how common is it to find glass on someone unrelated with crime. Interpretation of Physical Aspects of Glass Evidence Physical evidence has a tentative value if something could be true, for example, the glass could have come from the broken window. There can be an instance when the clothing of suspects examined for glass particles or other debris, of which the laboratory finds no traces. The failure of the physical evidence to bear out a suspicion does not necessarily indicate that the suspicion was wrong. RESULTS AND DISCUSSION Table 1. Observations by Four Students on Tops Observer Material Finding Taryn 1- Grey stripped vest top. 54% cotton 40% polyester 3% polyamide fiber NO GLASS 2- Grey wooly polo neck top. 38% polyester 3% Alsatian 2 PIECES OF GLASSES 3-Green long sleeve top 100% cotton NO GLASS Heather 1- Purple cardie pockets 75% payester 25% cotton NO GLASS 2- Purple jumper 100% cotton NO GLASS 3- Black vest top 95% cotton 5% elastane NO GLASS Scott 1- jersey T-shirt 100% nylon 3 PIECES OF GLASSES 2- Adidas T-shirt 100% polyester 1 PIECE OF GLASS 3- underarmor 63% nylon 23% polyester 14% elastine 1 PIECE OF GLASS ME 1- Yellow T-shirt 100% cotton NO GLASS 2- blue T-shirt 100% cotton NO GLASS 3- Yellow T-shirt 100% cotton NO GLASS Results showed that pieces of glasses were found on clothing with polyester or nylon as compared with clothing with cotton which reflects absence of glass fragments. Previous studies revealed that wooly clothing tend to retain glass fragments for longer time as compared to smoother materials like cotton cloth. Glass is usually analyzed in order to determine where did the impact force originate during the commission of the crime or event. The glass examination also look into the possibility that physical match exist between two or more pieces. And of course, the glass examination analyzes if two or more glass samples are consistent. A comparison of glass items requires a questioned and known sample be submitted. A tablespoon of fragments is usually adequate. Several simple tests are done on submitted items to verify that a sample is glass. If the sample is pliable or dissolves in water, it is not glass. After concluding a sample is glass, physical properties such as thickness, color, and fluorescence are observed. The refractive index is determined for glass particles using the double variation method. Temperature and specific wavelengths of light are variables plotted as data points on a graph. CONCLUSION Glass examination is a good method of determining the association of the evidence with the event. Glass fragments can be a physical evidence. The relationship between glass fragments and the event may have immediate or potential value in establishing the fact that a crime has or has not been committed. It may also indicate how a crime was committed or simulated. It can also show a connection or lack of connection between a suspect and a crime or show a connection or the absence of a connection between the victim and certain aspects of a crime. BIBLIOGRAPHY Almirall, Jose R., Trejos, Tatiana, Hobbs, Andria and Furton, Kenneth G. Trace elemental analysis of glass and paint samples of forensic interest by ICP-MS using laser ablation solid sample introduction, Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Defense and Law Enforcement II. Carapezza, Edward M. (ed.), Proceedings of the SPIE, vol. 5071, pp. 193-204, 2003. Caddy, Brian, The Forensic Examination of Glass and Paint: Analysis and Interpretation, J. Sci. & Justice, vol., 43, no. 3, pp. 175-176, Taylor & Francis, London, 2003. Curran, James M., The Statistical Interpretation of Forensic Glass Evidence. Internat. Statist. Rev., vol. 71, no. 3, pp. 497-520, 2003. Martin, Steve W., Glass, Discovery Channel School, Aug. 2001. Trejos, Tatiana, Montero, Shirly and Almirall, Jose R., Analysis and comparison of glass fragments by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and ICP-MS, J. Analytical & Bioanalytical Chem. Springer Berlin / Heidelberg, vol. 376, no. 8, pp. 1255-1264, Aug. 2003. . Read More