Trace Evidence Reading

In 1936 the wife of an NBC executive was killed in their Manhattan brownstone. She had been strangled with her pajama top and left in the bathroom. All indications were that she had known her killer, and when there appeared to be few clues except some twine used to bind her, a chemist was brought in to examine the crime scene.

In the bedroom he found only one strand, half an inch long, of stiff white hair, which he soon identified through a microscope as horsehair. Since two furniture movers had delivered a horsehair couch that morning and it was those men who reported the body, the detective in charge speculated that one of them had paid an earlier call. He identified the likely culprit and then found a connection via the piece of twine, because it had sufficiently distinctive markings to be traced to a manufacturer and distributor. It turned out that the same twine had been sold to the furniture store. Using this evidence to put pressure on the suspect, the detective got the confession he needed for conviction. This was one of the early cases where technology was used on material fragments to solve a murder.

Every person who is physically involved in a crime leaves some minute trace of his or her presence, and often takes something away. This is Dr. Edmond Locard’s principle of contact, proposed when he began his forensic laboratory in 1910. He closed a case two years later by examining what was under the fingernails of a female victim, and thereby showed how seemingly insignificant matter can make all the difference.

No matter how much someone tries to clean up a crime scene, something is generally left behind. It may not always be detected, but it’s difficult to take any kind of violent action without shedding something. This principle became the motivating factor in the development of forensic science.

An attorney displays fiber and hair evidence samples in court (AP)

While there is no end to the types of trace evidence that can be found, most investigations center on fiber or hair, which is easier to see than pollen or dirt. Cases involving those substances will be covered at length, but some of the more unique types of trace evidence that have helped to close cases are included as well.

Let’s look first at a controversial case involving fiber.

From 1979 to 1981, someone was killing Atlanta’s youth. More than twenty-five black males, some as young as nine, had been strangled, bludgeoned or asphyxiated. A few females were killed and some children were just missing, but all potential leads turned into dead ends. The only real clue – which was valuable only if a suspect surfaced – was the presence on several of the bodies and their clothing of some kind of fiber threads. A few also bore strands of what was determined to be hair from a dog.

The fiber discovery was reported in the newspaper and shortly thereafter, bodies were found stripped and thrown into the river. Some authorities surmised that the killer believed that the water would wash away trace evidence. They took it to mean that the killer (or killers) was paying attention to the media. (Others, however, did not think that all of these deaths were related.)

Wayne Williams (AP)

Only two days later, the police found what they believed had been the source of the splash – the body of 27-year-old Nathaniel Cater. He was dredged up about a mile from the bridge, and despite his murderer’s carefulness, a single yellow-green carpet fiber was found in his hair. (The assumption was that it had stuck there despite the water rather than thinking that he might have acquired it in the water.) Cater also showed signs of asphyxiation, but it was difficult to determine just how this had happened. Nevertheless, the medical examiner thought that he had been dead for at least two days.

The police got a search warrant for Wayne Williams’ home and car, and the search turned up a valuable piece of evidence: The floors of Williams’ home were covered with yellow-green carpeting, and he also had a dog. Comparisons from the samples removed from the victims showed good consistency with Williams’ carpet. Although Williams claimed to have an alibi, the description he gave of his movements the night they found him on the bridge was partly false and partly unsubstantiated. Three separate polygraph tests indicated deception on Williams’ part.

Then FBI experts analyzed samples from his rugs. With special equipment, and in consultation with DuPont, they managed to ascertain that the fibers came from a Boston-based textile company. The fiber was called Wellman 181B and it had been sold to numerous carpet companies. Each uses its own dye, so that made it possible to narrow down the likely source, which was the West Point Pepperell Corporation in Georgia. Their “Luxaire English Olive” color matched that found in Wayne William’s home. There were also similarities between the hair from Williams’ dog and the dog hair found on several victims.

However, many other homes had this carpeting installed, too. Thus, it had to be determined just how likely it was that Williams’ carpeting was unique enough to persuade a jury of his connection to the murders. The next step was calculating the odds.

A look into company records turned up information that they had only made that type of carpet during a one-year span of time, with over 16,000 yards of carpet distributed throughout the South. In comparison with the total amount of carpet distributed across the country, this was a very small sample. That made the statistical probability of the carpet being in any one person’s home to be slight, if it could be assumed that Luxaire English Olive had been fairly evenly distributed. Altogether they figured that around eighty-two homes in Georgia were carpeted with Luxaire English Olive. That meant the odds were stacked against finding many homes in Atlanta: 1 in 7792.

To make their case, the prosecution relied on only two of the twenty-eight suspected murders---the one from the river, Nathaniel Cater, and another recovered in the same general area a month before, Jimmy Ray Payne (although it had not been concluded that he had been murdered). A single rayon fiber had been found on his shorts, which was consistent with the carpeting in Williams’ station wagon. In this second case, statistical probability was also employed. With Chevrolet’s help, the investigators determined that there was a 1 in 3,828 chance that Payne had acquired the fiber via random contact with a car that had this carpeting installed.

When the odds in both cases were multiplied, the law of probability that both men could have picked up these fibers in places other than Williams’ home and car came out to 1 in almost 30,000,000. That seemed pretty staggering.

The prosecution also introduced into evidence the fibers found on the bodies of ten of the other victims (allowed in Georgia courts), which also matched those in Williams’ car or home. These, they claimed, showed a pattern, and taken altogether, it increased the odds in the fiber evidence into numbers that no one could even comprehend. In total, there were 28 fiber types linked to Williams. In addition, several witnesses had come forward to place Williams with some of the victims, and others claimed to have seen suspicious scratches on Williams’ arms.

After only twelve hours, the jury returned a guilty verdict, with two life sentences. The police announced that twenty-two of the unsolved murder cases were now closed, despite the fact that there was no real proof for those victims.

Subsequently the Williams conviction has become controversial. To understand this, let’s look at how fiber analysis is done.

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 with – sometimes 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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.

In 1990 in Telluride, Colorado, Eva Shoen’s young daughter found her dead from a single gunshot to her head. Her husband, Sam, came under suspicion, but he truly appeared to be the grieving, shocked husband, a victim of random violence. The police were confident they would solve the case, because the bullet taken from Eva’s skull had the distinct markings of a particular type of pistol. However, the case eventually found its way into the cold cases file. There just were no leads.

Three years later, the Telluride police received a call from a man in Arizona who believed that his own brother, Frank Marquis, had been the perpetrator. Marquis had once confessed this crime, but an attempt to trap him during a phone conversation failed. Nevertheless, when the gun was recovered, an arrest seemed a sure thing. Unfortunately, Marquis had covered his tracks all too well, including tampering with the barrel of the gun so that the bullet fired from it could not be matched. All they had on him was a hearsay conversation.

However, tracing Marquis’ movements indicated that he had indeed been in Telluride during that weekend for a festival, and that he had a police record for rape. This was the man, the detectives felt, and they had to find a way to get him. Putting pressure on Marquis’ travel companion, they learned that at some point along the road back, Marquis had tossed two bundles out the window of the car. They suspected that this was the clothing he had worn to commit the crime. Still, it was a long and winding road between Telluride and the point where Marquis had ended his journey some four hundred miles away.

Detectives scoured the roadway until they narrowed the possibilities down to four places. As luck had it, a construction crew had recently moved a pile of dirt, exposing a bundle of clothing that the dirt had preserved. On the shirt was a single strand of hair, which was examined in the lab against a sample taken from Eva Shoen. Forensic trace expert Joseph Snyder analyzed the color and structure, and pronounced them a close match.

When the investigators told Marquis of their findings, he confessed. It was a bungled burglary, he said, indicating his knowledge of the plea-bargaining system. Although the officers in charge of the case believed that he had in fact planned to rape Eva Shoen and had killed her in the process, they knew that this would be impossible to prove. Marquis got a sentence of twenty-four years for manslaughter.

Sometimes a single strand of hair will make all the difference between a case closing down and a lead that opens it in an entirely new direction.

Is the analysis really that sophisticated or does it just bolster a good guess? To answer that question, we need to examine the technology.

Like fibers, hair specimens are also understood in forensic research as “class characteristic.” At best, a hair may have enough similar properties compared with a known sample to be “consistent with” the sample; it can’t be said definitively to be a perfect match. While hair samples can be used to exclude a suspect, as with a Caucasian hair excluding black perpetrators, they can only be considered as contributing evidence.

In homicide cases, hair is picked up at the scene and is generally collected from several different parts of the body, including several areas of the scalp. Because different hairs on the same person can show many variations, the larger the sample for analysis, the better. An average sample ranges from 24 to 50 pieces, although those samples on which DNA can be done can be much smaller.

Human Cells (AP)

Hair analysis can indicate whether the source is human or animal, and also whether the source is a member of a particular race. It can determine if the hair has been dyed, cut in a certain way or pulled out, and where on the body it was located. In some cases, evidence of poisoning shows up in the hair. The hair shaft with a follicle can also offer genetic determinations, such as blood type or DNA, and since the external layer of the shaft resists decomposition, it’s the kind of evidence that has real staying power.

Vernon J. Gerberth, in Practical Homicide Investigation, points out that hair (and fiber) evidence is useful in:

1. Helping to establish the scope of the crime scene
2. Placing a perpetrator at a scene
3. Connecting a suspect with a weapon
4. Supporting witness statements
5. Connecting crime scene areas (abduction, vehicle used, dump site)
    

Forensic analysis of hair centers on color and structure, determined through microscopic magnification. If the hair has been pulled out, it should include the follicle, and that helps to see the hair’s full length. The shaft has three forensically relevant layers: the cuticle, cortex, and medulla. The cuticle has overlapping external scales, which helps in species identification: Animals are different from humans. Within the cuticle is the cortex, made up of spindle-shaped cells that contain the color pigment, and the way the pigment is distributed helps to identify hairs from particular individuals. The center of the shaft is the medulla, which is also valuable for species differentiation: An animal’s medullary index (diameter relative to the shaft’s diameter) is larger than a human’s. However, the medulla is often fragmented or interrupted, and may differ from one hair to another on the same person.

Negroid hairs are kinky, with dense pigments, while Caucasian hairs are generally straight or wavy, with finer pigmentation. Pigment distribution is also different between the two races. The hair of an infant or young child tends to be finer than adult hair, but it is difficult to establish gender from hair samples. Hair that has follicle tissue was probably pulled out, and that tissue offers the possibility of DNA analysis through the PCR method (which recreates the DNA molecules).

In the 1950s, a technique called neutron activation analysis became a valuable forensic tool. A sample such as hair is bombarded with neutrons while inside the core of a nuclear reactor. The neutrons collide with the components of the trace elements and make them emit gamma radiation of a characteristic energy level. That way, the scientist can measure every constituent part of the sample, no matter how small. In a single hair, for example, fourteen different elements can be identified.

The first case to utilize neutron activation analysis was the 1958 murder of 16-year-old Gaetane Bouchard in Canada. Her former boyfriend, John Vollman, lived across the border in Maine and he was seen with her just before she was discovered dead. Flakes of paint from the place where they had been together were matched to his car. Also, the victim’s color of lipstick was found on candy in his glove compartment. However, it was the strands of hair found clasped in the victim’s hand that ultimately convinced the jury. These were matched to Vollman via a ratio of sulfur radiation to phosphorus, which was closer to his ratio than hers.

As forensic science advances with computers and increasingly more accurate means of detecting the component parts of small samples, trace evidence may soon play even more significant roles. As it is, the more trace evidence an investigator can collect at a crime scene, the better the chances of making a case.

Although hair and fiber are currently the most frequently analyzed trace evidence, there are other types that ought to be noted. A few have offered important clues for solving a crime.

Crime scene examiners are looking for anything, no matter how minute, that appears to be foreign to the place. Aside from hair and fiber, along with other bodily secretions, there are more items that can come under scrutiny. Any object or substance becomes evidence if it can be identified as not naturally belonging to a scene and then linked with a suspect. Databases for comparison are maintained in most large forensic labs, with the most extensive collection for many types of trace evidence located at the FBI.

Among the most common substances for trace analysis are:

Glass:         When product tampering made national news in the 1980s, some consumers placed glass fragments in jars of baby food in the hope of a monetary settlement. Analysis of the fragments indicated that each type of contaminant was from a different source, so this “crime spree” was unlikely to have been the work of a lone tamperer. Glass is a solidified liquid that has unusual properties. If a perpetrator smashes glass, some tiny slivers will adhere to his clothing, even after it has been cleaned. Glass identification involves a complex microscopic examination that measures the “refractive index,” calculated from the angle at which a ray of light hits the surface. Pieces of glass may also be analyzed through spectrography or neutron activation, and glass shatter patterns have provided important clues about how an event took place.

Dirt/dust:       Particles picked up on a suspect’s clothing can sometimes reveal where he or she has been, and the same goes for where a corpse has been, which helps to determine whether a murder victim has been moved. Plant spoors, insects, and other microorganisms that are revealed under the microscope provide clues. Dust particles generally yield something about their origins, whether from a concrete floor, bricks, cement, or a particular room. They might offer leads about where someone lives or works. The 1960 murder of 8-year-old Graeme Thorne was partly solved by traces of pink mortar found on his clothing. A house with pink mortar was located, and further evidence was found to close the case and convict the killer.

Palynology:    This is the study of palynomorphs, or pollen data, trapped in or found on materials associated with a crime. Because of their predictable production and dispersal rates in specific regions, they can help to link a suspect to the scene of a crime. In fact, palynologists believe that both legal teams missed a bet in the O.J. Simpson case by failing to look into pollen. If Simpson was present at the crime scene, and had hidden in the bushes as was suggested, his clothing might have picked up pollen spoors. If not, then this would have been important evidence in his defense. The earliest cases in this field were in the sixties. A 1969 murder investigation in Sweden used the presence of pollen in the dirt found on the body to show that she had been killed in a spot other than where she was found. In an Austrian case, mud on a murderer’s boots linked him to a crime scene, and he confessed. One detective even found pollen in the grease of a killer’s gun, and another found pollen in the ink of a document that demonstrated that it was a forgery.

Paint:             The techniques used for glass analysis are also employed for paint chips. Chips from cars can be compared to samples in the National Automotive Paint File, which holds more than 400,000 samples. Undercoats help to narrow down the possible manufacturers. Also the shape of a chip can be matched to an area where a chip is missing, and its chemical constituents can be analyzed via releasing the gases and using gas chromatography. That creates identifying characteristics for each layer and establishes points of comparison. A trace of yellow paint was found in a spot where a rapist had hidden his car was traced to a specific model. When a suspect was located through a computer database that included those cars, his vehicle showed the scrape at the appropriate height. With the police on his trail and evidence accumulating, he confessed and was sent to prison.

Seeds:             In the 1960 murder of Graeme Thorne, seeds from a rare type of cypress told investigators that the body had been moved from the murder site. A cypress tree found in a garden of a house that also matched mortar found on the body pointed the police in the right direction. Further evidence built a solid case against Stephen Bradley, who was convicted. Like pollen analysis, knowledge of plant life peculiar to certain areas can offer important information for making decisions in criminal investigations.

Other types of evidence and modes of analysis may be lumped under the category of “trace evidence,” but the information presented here shows the basic principles: Collect apparently foreign matter from a crime scene or body, and use the best method for measuring the most clearly identifying characteristics. That information, when compared with similar substances associated with a suspect, can corroborate other types of evidence and help to build a case. Right or wrong, juries have convicted on trace evidence alone, and responsible forensic investigators will try to make sure that it truly proves what they claim.