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.
A compound microscope uses light reflected from the surface of a fiber and magnified through a series of lenses, while the comparison microscope (two compound microscopes joined by an optical bridge) is used for more precise identification. A different device, the phase-contrast microscope, reveals some of the structure of a fiber, while the various electron microscopes either pass beams through samples to provide a highly magnified image, or reflect electrons off the sample's surface. A scanning electron microscope converts the emitted electrons into a photographic image for display. This affords high resolution and depth of focus.
Another useful instrument is the spectrometer, which separates light into component wavelengths. In 1859, two German scientists discovered that the spectrum of every organic element has a uniqueness to its constituent parts. By passing light through something to produce a spectrum, the analyst can read the resulting lines, called "absorption lines." That is, the specific wavelengths that are selectively absorbed into the substance are characteristic of its component molecules. Then a spectrophotometer measures the light intensities, which yields a way to identify different types of substances.
A combination of these instruments for the most effective forensic analysis is the micro-spectrophotometer. The microscope locates minute traces or shows how light interacts with the material under analysis. Linking this to a computerized spectrophotometer increases the accuracy. The scientist can get both a magnified visual and an infrared pattern at the same time, which increases the number of identifying characteristics of any given material.
The first step in fiber analysis is to compare color and diameter. If there is agreement, then the analysis can go into another phase. Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents. Under a microscope, the analyst looks for lengthwise striations or pits on a fiber's surface, or unusual shapes---as with the one short and two long arms of the trilobal fibers in the Williams case.
In short, the fiber analyst compares shape, dye content, size, chemical composition, and microscopic appearances, yet all of this is still about "class evidence." Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source, and there is no fiber database that provides a probability of origin.
Since the Wayne Williams case pretty much came down to fiber evidence, it's obviously open to serious challenge. Chet Dettlinger is a former assistant to the Atlanta Chief of Police. He and a group of other high-ranking ex-law-enforcement officers independently investigated the case. Dettlinger, now a Georgia attorney, was asked by Williams' defense lawyer, Al Binder, to act as a consultant, and he co-authored, The List, the only book to be published on the case. Among other problems, he saw glaring errors with the way the fiber evidence was presented.
"The 'matching' fibers were taken only from victims," he says. "Only one individual red cotton fiber was found at the Williams home--which can be found in abundance at K-Mart or Walmart---which is similar to fibers in victim Michael McIntosh's underwear. That came from the vacuum sweepings of a car, which the Williamses may or may not have owned at the time that McIntosh was murdered. Not one fiber from any victim was found anywhere near the carpet in the Williams' house.
"Insofar as the Wellman fiber is concerned, they were attempting to demonstrate how rare the fiber in the carpet in 'Wayne Williams' room' was. This ignores the fact that all of the Williamses, and any regular visitor to the home, existed in the same environment."
Dettlinger goes on to pinpoint the central errors in the prosecution's probability analysis as:
- They ignored the fact that the same carpet was in all but one or two rooms in the house, including the parents' bedroom and the living room.
- They overlooked the fact that Wayne Williams had changed rooms since the last murder on their list. The room they identified as his was actually used by a relative.
- They ignored the fact that even in residential applications many of the exact same fibers were dyed the same color and used in rugs which are not the same model number as those used in the Williams' house.
- They chose to narrow their analysis to a statistical area that doesn't exist--the southeast. They also failed to allow for the possibility that the killer or killers lived elsewhere and traveled regularly to the area.
- They included only fibers said to have been used in carpets for residential applications, ignoring the fact that the same fiber could be found in many apartments and businesses.
- They ignored the fact that millions of pounds of the exact same fiber had been sold undyed to other manufacturers for use in applications such as car mats.
About the finer probability ration involving the car, Dettlinger points out that "the prosecution used metro Atlanta figures to show how rare this vehicle would be. This means the Williamses' vehicle was not included because it was registered in Muscogee County, which is far from Atlanta."
In addition, since four people had been in the Williams home regularly, that made four suspects, not one. "The prosecution summed up by saying that even though the fibers were common, it is the combination of fibers which could not be found in any other environment except the Wayne Williams environment. This gives us four or more suspects, not one, and more importantly: What about a Laundromat where the environments of hundreds, perhaps thousands of fibers are mixed and even clogged together in filters? Clifford Jones was killed in the back room of a Laundromat.
"Clifford Jones was the final blow to the state's fiber case. He was one of only seven who had the even remotely-unique Wellman fiber. However, both the FBI and the investigating officer agree with me that Jones was killed by someone other than Williams and the Jones case was not introduced at the trial even though the defense begged for its submission."
Clearly the fiber probability ratio was not as impressive as it seemed.
This case was the first to have relied on this type of analysis for pivotal evidence, and several appeals justices noted that it was too weak: There were no eyewitnesses, weapon, motive, confession, or clear placement of Williams with any of the victims prior to their deaths. Exactly what did this evidence corroborate? It was not even that clear that the two victims had been murdered, and both were adult males---completely unlike any of the young boys used in the ten "pattern" cases. It seems obvious from the many problems in this case that fiber alone should not be a deciding factor.
The same can be said for shafts of hair that have only basic distinguishing characteristics. Nevertheless, trace evidence does have its place, as seen in the following investigation.