How does a crime lab study in CSI?

How does a crime lab study in CSI?

Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: What is a 'mobile crime laboratory'?; What physical evidence is important for an investigator to collect at a crime scene?; What evidence should a forensic scientist collect from the body of a murder victim? and more...

A crime lab basically examines physical evidence for either one of two purposes: either to identify the physical evidence as "What is it?" Is it white powder? Is it heroin? Is it cocaine? That is what we would call the identification or the "What is it?" The other function of the crime lab study is to compare physical evidence to determine whether two or more objects emanate from the same source. Now, for example, if a fingerprint is left at a crime scene and we have a suspect and one of the prints on that suspect's fingers compares to the print left at the crime scene, we have made a comparison and we have determined that that individual and no other individual was present at the crime scene. We call that "individuality", and the ability to compare and to link a person or a thing to a crime scene to the exclusion of all other persons or things.