Notes From CS Undergrad Courses FSU
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Locards exchange principle states that the perpetrator of a crime will always bring something into the crime and leave with something from it. Dr. Edmond Locard was a pioneer in forensic science who formulated the basic principle that, "Every Contact leave a trace". As Paul L. Kirk expressed this principle.
Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibres from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.
Trace evidence is any material left at a crime scene as a result of contact between two surfaces, for example, shoes and the floor covering soil.