Formulated by Frenchman Edmund Locard, it states that when a subject comes into contact with an object or another person, a cross transfer of evidence occurs. Hairs and fibers are easily shed. Thus, the strands found on an individual will reflect the most recent environmental contact. Positive identification from a specific source is usually not attained by hair analysis. Techniques using DNA in the human hair root or in follicular tissue adhering to pulled hair are being researched.
Analysis can associate a hair to a person based on microscopic characteristics in the hair.
Moreover, hair analysis provides valuable exclusionary evidence. The value of fiber evidence depends on the ability to narrow the origin to a limited number of sources or to a single source. Comparison could establish whether there are links between suspect and victim or suspect and crime scene. The type of fiber, the fiber composition, fiber construction and fiber color can be determined by fiber analysis.