Can fiber and hair analysis really solve crime?

Among the list of “scientific” techniques often put forward as reliable in solving a crime is fiber and hair analysis. According to scientists and experts, however, this process is not one that can conclusively point to a crime’s perpetrator, and its use has resulted in previous wrongful convictions.

Fibers are small units of textile material that occur naturally, like wool or cotton, or synthetically such as nylon and polyester. In forensic science, fibers are considered “trace evidence” and are used to determine a contact between garments. In the late 1900’s, French scientist Edmond Locard, discovered that “people transferred fibers and other trace materials without being conscious of it”, leading him to develop the Lucard’s Exchange Principle. 

During investigations of crime scenes, fibers, like those from a piece of clothing, drape, bed sheet, or other material, can be found on a victim or at a crime scene. Once a fiber is located, it is analyzed in a lab and compared to suspected sources. Analysts examine the sample to compare fiber type, color, environmental conditions, and other details. However, none of these observations can conclusively determine the exact, specific source of a single fiber; the comparison can only determine whether a sample fiber is associated with the same fiber class. 

According to a 2002 publication from the Federal Bureau of Investigation’s Forensic Science Communications, “in order to say that the fiber originated from the item of clothing, the clothing either had to be the only fabric of its type ever produced or still remaining on earth, or the transfer of fibers was directly observed… It can never be stated with certainty that a fiber originated from a particular garment because other garments were likely produced using the same fiber type and color.”

Relying exclusively on fiber analysis to convict a person of a crime can lead to wrongful convictions. Over-relying on fiber analysis results may also lead investigators to become tunnel visioned, focusing on one suspect because of what a fiber analysis suggests while ignoring other potential suspects that deserve investigation. 

In 1993, Michael Blair was convicted of murder and sentenced to death in Texas. Michael’s conviction was largely based on hairs found on Michael’s car that “were similar” to the victim’s and that the “chemical makeup of fibers from a stuffed animal in Blair’s car resembled fibers found on the victim’s body, with only “‘subtle differences.”’ He served 14 years and was sentenced to death before being exonerated by DNA evidence. 

According to the Minnesota Department of Public Safety’s Bureau of Criminal Apprehension, fiber examinations are still carried out to date. Further, neither Minnesota, North Dakota, nor South Dakota are one of the six states that have enacted the ‘Changed Science’ Statute allowing convicts to get back into court if convictions were based on discredited forensic science. 

While fiber and hair analysis may support investigations in narrowing in a suspect, investigators must be aware of the tactic’s limitations and be mindful of the cognitive bias that can result, leading them to focus on a particular suspect artificially. Better understanding of fiber and hair analysis, and its significant limitations, by criminal legal professions is critical in preventing wrongful convictions and solving violent crime.