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.

"An easier way to remember this is that 'Every Contact Leaves a Trace.'"
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