Most trace evidence found at a crime undergoes forensic analysis for two main purposes: identification and comparison. Often tiny strange particles are found, and testing for identification purposes establishes exactly what the material is. Obviously, this is a vital step in determining if questionable substances left at a crime scene are traces of blood, illegal drugs, or if hairs collected are human or animal. Comparisons attempt to determine if the evidence found at a scene shares a common origin with that from a suspect. For example, crime-scene fibers would be compared with fibers from clothing, carpets, etc. of a suspect, to see if they match. (Lyle, 2004).The primary significance and most valuable characteristic of trace evidence is it can unknowingly be transferred from one person to another, or between a person and crime scene. During the commission of a crime, tiny particles of items such as hair, fibers, dirt, blood, skin or saliva from a perpetrator are transferred to clothing, hair, etc. of a victim, or vice-versa. This evidence is vital, as often it is the only thing that connects suspect to the crime scene and was first brought to the attention of investigators in the early 1900s, by Edmond Locard, a French police officer. This is the real cornerstone of forensics and known as Locard's Exchange Principle. (Lyle, 2004).Two types of trace evidence often recovered at crime scenes are hair and fibers. While in most cases, evidence of this nature cannot conclusively identify a particular person, it is a valuable source of associative evidence.
[...] The width of medulla relative to overall diameter Hair and Fiber 3 of hair shaft is called the medulla index and normally expressed as a fraction. This index, in most animals, is greater than or half the thickness of the hair. The medulla in humans is usually narrow and has an index of Presence and appearance of medulla vary in different individuals and within same person, therefore, if medulla appears continuous, interrupted or fragmented helps determine hair's species of origin. [...]
[...] Analyzing fiber evidence Fibers, like hair is wonderful trace evidence as it is easily shed, sticks to skin or garments and is transferred between a crime scene and people, clothing, home, car, etc. Tracing the source or identifying the manufacturer of fibers found at a crime scene, is investigators' objective. Hair and Fiber 5 Fibers fall into three basic groups:Natural: Derivative of animal, plant or mineral origins. Microscopic examination can easily identify and make comparison of fibers. Manufactured or Man-made: Made from derivatives of cotton or wood pulp, which is dissolved and cellulose extracted. [...]
[...] Hair and Fiber 4 Additional techniques of forensic hair analysis such as neutron activation analysis can be used to detect over a dozen different chemicals that may be in one's hair. Rarely would hair from two people have precisely the same chemicals, making crime-scene evidence and suspect samples easier to match. Examinations can also disclose what area of the body a hair came from and in certain cases reveal race and establish if hairs were forcibly removed, or simply fell out. [...]
[...] Hair and Fiber 6 Scanning electron microscope, Used when fiber or fabric is damaged. The subtle structural details can be uncovered and expose how the damage happened.Two other procedures are often used–SEM combined with dispersive ray spectrometer (SEM/EDS) and gas chromatography with mass spectrometry (GS/MS) can produce chemical composition, separate and identify the chemicals of fibers and pigments added during or after manufacturing process. These help identify manufacturer or source of fiber. (Lyle, 2004). Collecting and preserving fiber evidence: Like hair, fiber evidence must be handled with scrupulous care to avoid potential cross-contamination. [...]
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