The Atlanta Child Murders
Cross transfers of fiber often occur in cases in which there is person-to-person contact, and investigators hope that fiber traceable back to the offender can be found at the crime scene, as well as vice versa. Success in solving the crime often hinges on the ability to narrow the sources for the type of fiber found, as the prosecution did with their probability theory on the fibers in the Williams case.
The problem with fiber evidence is that fibers are not unique. Unlike fingerprints or DNA, they cannot pinpoint an offender in any definitive manner. There must be other factors involved, such as evidence that the fibers can corroborate or something unique to the fibers that set them apart. For example, when fibers appeared to link two Ohio murders in the 1980s, it was just the start of building a case, but without the fibers, there would have been no link in the first place.
In 1982, Kristen Lea Harrison was abducted from a ball field in Ohio and her body was found six days later some thirty miles away. She had been raped and strangled. Orange fibers in her hair looked suspiciously like those that had been found on a twelve-year-old female murder victim from eight months earlier in the same county. Since they were made of polyester and were oddly shaped (trilobal), forensic scientists surmised that it was carpet fiber. In addition, a box found near Kristin's body and plastic wrap around her feet indicated that the killer had once ordered a special kind of van seat, but then leads dried up.
Some time later, a 28 year-old woman was abducted and held prisoner in a man's home. He tortured her and appeared to be intent on killing her. When he left, she escaped and reported him. Police noticed that he had a van similar to the one into which Kristin had been forced. It proved to have orange carpeting that matched the fibers in her hair. The color was unique, which allowed scientists to trace it to a manufacturer who supplied information about its limited run. Apparently only 74 yards of it had been shipped to that area of Ohio. That helped to narrow down possibilities. Other evidence established a more solid link and Robert Anthony Buell, was eventually convicted.
Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. For analysis, they are first determined to be natural, manufactured, or a mix of both.
Natural fibers come from plants (cotton) or animals (wool). Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers. To determine the shape and color of fibers from any of these fabrics, a microscopic examination is made. Generally, the analyst gets only a limited number of fibers to work withsometimes only one. Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home, and the fibers are laid side by side for visual inspection through a microscope.