Although physical evidence cannot provide for a positive identification of a suspect, lab examination may narrow the origin of the evidence to a group that includes the suspect. The comparison of trace evidence depends upon detection with the human eye, aided by use of microscopes. However, when it is properly collected at the crime scene, hair can provide strong corroborative evidence for placing an individual at a crime site. The most common request at a crime lab is to determine whether or not hair recovered at a crime scene compares to hair removed from a suspect. In comparing hair the criminalist is most interested in matching color, length, and diameter.
Natural fibers are from animals or plants.
The most prevalent plant fiber is cotton and when viewed microscopically its most distinguishing feature is a ribbon-like shape with twists at regular intervals. Nylon came along in 1939. Now the manufactured fibers are so numerous that they are given generic names such as polyester, spandex, acrylic, etc. Most of the fibers currently manufactured are produced from synthetic chemicals and are classified as synthetic fibers. The microscope remains the most important means for identifying and comparing paint specimens.