Fiber analysis is the identification of small pieces of material that have separated from the whole. In legal investigations, examination of these fibers often fall under the jurisdiction of the trace evidence department. This form of analysis is often referred to as forensic fiber analysis and is generally used to provide clues to crimes or support conclusions drawn by other evidence.
It is widely accepted that some trace evidence exists at virtually every crime scene. Contact with the victim or the surroundings often causes small amounts of material to be transferred either to or from the suspect. The field of forensic fiber analysis examines the evidence that involves manufactured materials.
Although a large part of fiber analysis focuses on textiles, the reality is that most man-made products have the potential to break apart into smaller pieces. Carpeting, clothing, and upholstery fibers are obviously fairly common in trace evidence. Somewhat surprisingly, fibers from paper, toothbrush bristles, and even baby diapers have also been studied.
Analysis incorporates many stages. The first priority is generally to determine what kind of materials are contained in the fiber. Once that is determined, any special properties of the fiber, such as dyes or other chemical treatments, are examined. Often, answering these two questions can help identify the source of the fiber.
Then, the evidence needs to be put into context. In the example of baby diaper fibers, investigators first eliminate the possibility of the victim coming in contact with the fiber from a source other than the suspect. It that turns out to be the case, then certain speculations may be made about the suspect that could narrow the scope of the investigation. For instance, if the suspect was in a relationship with a person who worked in a factory that made diapers, that person would obviously come under closer scrutiny.
Forensic fiber analysis becomes more concrete when a possible source for the fiber is found. Comparison with the donor object can provide confirmation that the object was at the crime scene. Fiber analysis technicians can also determine how the fiber was removed from the whole. By examination of the ends of the fiber, they can learn whether it was torn, cut, or simply eroded away from its source. This can be an important tool in recreating the events of a crime.
Fiber analysis is a valuable tool, but it rarely provides the bulk of evidence in criminal investigations. The presence of red wool fibers at the scene of a murder does not mean that everyone associated with the victim who happens to own a red wool sweater becomes a suspect. However, if the fibers are similar in composition to the blood-covered sweater of a suspect, then the finding provides supporting evidence of that person's guilt.