Examining Biological Evidence at a Crime Scene
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In examining biological evidence at a crime scene, the focus is on the identification and individualization of human tissues (Forensic, 2005, 227). This includes the analysis of blood, semen, saliva, feces, hair and abortion products. The first method employed to analyze DNA from crime scenes was restriction fragment length polymorphism (RFLP), which uses a restriction enzyme to cut DNA into smaller fragments separated by size using gel electrophoresis, transferred from the gel to a solid membrane, exposed to labeled DNA fragment probes, then exposed to a film and the final image is known as an autoradiograph. This test had many disadvantages, including needing sufficient sample for analysis, and has since been replaced by the PCR test, in which short tandem repeats are amplified to sufficient numbers for more accurate analysis then visualized in the same way, though the process is now fully automated so that a full genetic profile of a DNA sample can be matched to a known sample from a particular individual and this method is now widely accepted as evidence that the DNA came from a particular donor. Forensic laboratories analyze physical evidence and use quality assurance programs designed to ensure the reported results are scientifically valid and the opinions are based only on the results that are considered reliable (Class, 2005). Trace evidence includes such evidence as fibers, hairs, body fluids, paint, glass, soil, and plant debris (Forensic, 2005, 228). Speci
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nd stabbing. Satellite spattering occurs from dripped blood. Castoff spatter will occur from a weapon swung repeatedly. Transfer blood can be found on weapons. Arterial spatter patterns are easy to identify where an artery has been cut. Skeletonized bloodstains occur in the central area of a dried bloodstain where the center has been wiped in some way. Expirated bloodstains can also be found at some sites.
Shoes may leave patent and latent two-dimensional impressions caused by dust, dirt, grease, oil, blood etc. picked up on the shoes by walking on hard surfaces such as tile, linoleum or wood flooring (Forensic, 2005, 361). Impressions of shoe prints can be found in soft surfaces such as mud, snow, sand and soil, leaving a three-dimensional impression. The contact between the shoe and the substrate results in a transfer of class and individual characteristics from the shoe to the impression it leaves, and the forensic examiner looks at both of these characteristics to determine if a specific item of suspect footwear made the crime scene impressions, or if the item can be eliminated as crime scene evidence. Footwear impressions are used routinely to prove a suspect was present at a crime scene, and this evidence is
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Approximate Word count = 1923
Approximate Pages = 8 (250 words per page)
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