Trace evidence is very important in forensic investigations. This category of evidence encompasses many diverse types of microscopic materials as well as some examples that are easily visible to the naked eye. The subject is broad and diverse because of the number of different types of evidence that are commonly encountered. Trace evidence can be thought of as evidence occurring in sizes so small that it can be transferred or exchanged between two surfaces without being noticed. Varieties of trace evidence can include, but are not limited to: metal filings, glass fragments, feathers, food stains, building materials, lubricants, fingernail scrapings, pollens and spores, cosmetics, plastic fragments, gunshot residue, chemicals, paper fibers and sawdust, human and animal hairs, plant and vegetable fibers, blood and other body fluids, asphalt or tar, vegetable fats and oils, dusts and other airborne particles, insulation, textile fibers, soot, soils and mineral grains, and explosive residues. .
Forensic scientists routinely come into contact with a relatively few number of these. They are: hair, glass, paint, fibers, fingerprints, and flammable liquids. These will be covered more in-depth in this paper. .
Edmond Locard, a French scientist and one of the early pioneers in forensic science believed strongly that individuals could not enter an area without taking dust particles with them from the scene. This became known as what is now called "Locard's Exchange Principle." This principle states that when two objects come into contact with each other, each of the objects will leave particles of one on the other. It is this principle that is the foundation of the forensic study of trace evidence. .
Trace evidence examination is the examination and analysis of small particles in order to help establish a link between a suspect and a crime scene or a suspect and the victim of a crime. These small particles usually include such items as hair, paint, glass, and fibers.
