what are some key steps in securing and identifying both physical and biological evidence at a crime scene?
A successful crime investigation depends upon the collection and analysis of various kinds of evidence. Forensic scientists classify evidence in different ways and have specific ways of dealing with it. [ One major distinction is between physical and biological evidence. Physical evidence refers to any item that comes from a nonliving origin, while biological evidence always originates from a
living being. The most important kinds of physical evidence are fingerprints, tire marks, footprints, fibers, paint, and building materials. Biological evidence includes bloodstains and DNA.
Locard's Exchange Principle dictates that evidence, both physical and biological, is to be found at the scene of a crime because the perpetrator always leaves something behind by having contact with victims and objects there. Similarly, he or she will often take something away with them, which can be found on a search of their person, their garment, a vehicle, or their premises. Such evidence is often found in minute quantities and known as trace evidence. One important source of physical trace evidence is textile fibers, which usually comes from clothing or furniture involved in the crime. It may either be left behind by the perpetrator or picked up from the victim. Typically, trace evidence is invisible to the naked eye and is collected by brushing or vacuuming a suspect surface. Once collected and back in the laboratory, microscopic techniques will often be used in its examination and analysis as, for example, in the case of paint fragments or textile fibers. ]
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