|FORENSIC LOCARD'S PRINCIPLE|
Locard's exchange principle
Locard was the director of the very first crime laboratory in existence, located in Lyon, France. Locard's exchange principle states that "with contact between two items, there will be an exchange" (Thornton, 1997).
Essentially Locard's principle is applied to crime scenes in which the perpetrator(s) of a crime comes into contact with the scene, so he will both bring something into the scene and leave with something from the scene. Every contact leaves a trace.
Fragmentary or trace evidence is any type of material left at – or taken from – a crime scene, or the result of contact between two surfaces, such as shoes and the floor covering or soil, or fibers from where someone sat on an upholstered chair.
When a crime is committed, fragmentary (or trace) evidence needs to be collected from the scene. A team of specialized police technicians go to the scene of the crime and seal it off. They both record video and take photographs of the crime scene, victim (if there is one) and items of evidence. If necessary, they undertake a firearms and ballistics examination. They check for shoe and tiremark impressions, examine any vehicles and check for fingerprints.
Each item found as evidence is put into a sterilized container (contrary to popular belief, this is almost never a plastic bag, but actually a paper bag or envelope, which will prevent further decomposition of evidence) and labeled for later analysis at the laboratory.
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