In the Crosshairs: Why the Forensic Science of Hair Analysis Isn't Foolproof
It was a little after 3 a.m. on July 26, 1978—a typically muggy summer night in Washington, D.C.—when John McCormick returned home from working the night shift. As the 63-year-old taxi driver walked up the steps to his front porch, a man in a stocking mask emerged from the darkness and pointed a gun at him. Inside, McCormick’s wife Belva heard shouts—and the sound of a gunshot. She called the police, who arrived in time to find McCormick shot to death with a single bullet. The gunman had vanished.
Investigators found the stocking mask a few feet away from the house. The assault was the second shooting in the neighborhood in a month, and no one could say for certain if the killings were related.
Later, an informant told police that she thought a local 17-year-old named Santae Tribble might have owned a gun similar to the .32-caliber believed to have been used (the actual weapon was never recovered). But the only physical evidence connected to the crime was the mask—and the 13 hairs attached to it.
Microscopic analysis was the best way to analyze hair evidence available at the time, and it dominated the physical evidence presented at Tribble’s trial. An FBI analyst testified that one of those hairs matched Tribble’s “in all microscopic characteristics.” In its closing statement, the prosecution told the jury that there was “one chance in 10 million” that the hair could have belonged to someone other than Tribble. He was convicted in 1980 and sentenced to 20 years to life.
Santae Tribble maintained his innocence, and in 2012, mitochondrial DNA testing of the hairs proved that none had belonged to Tribble—they had actually come from three different, unrelated people and a dog. After spending more than two decades in prison for a crime he didn’t commit, Tribble was fully exonerated.
Following Tribble’s case, the FBI ended its hair analysis program and began a review of past cases. But even today, the public still perceives microscopic hair analysis to be virtually foolproof, a belief driven by historical cases and crime shows.
The Trouble With Microscopic Analysis
Hair's long history of use as forensic evidence dates back to an 1855 murder trial [PDF]. After that case demonstrated the value of hair analysis, police in Europe called in medical pathologists to use their microscopes to look at hair samples. But drawing useful conclusions with limited experience—and limited magnifying power—was often difficult. Microscopes were much simpler than today’s models, with less magnifying power and rudimentary light sources, and medical pathologists were trained to look for the symptoms of disease, not the particular characteristics of crime suspects.
But as forensic science developed further, the analysis of hair emerged as a field as its own right. Eventually, it started popping up on TV shows like Law & Order and CSI: Crime Scene Investigation— and the misconceptions about what hair analysis could actually achieve took off.
“People watch a TV show and they see someone take a hair from a crime scene, and they put it in a flatbed scanner, and all of [a] sudden, people’s faces pop up on the screen,” says Jason Beckert, a microscopist at Microtrace, a materials analysis laboratory in Elgin, Illinois. His real-world work is very different, and often complements other types of physical evidence analysis.
People often confuse microscopic analysis and DNA analysis, but the two techniques give investigators different kinds of information. The microscopic analysis that Beckert performs is most often used to provide contextual clues in investigations—it's a visual comparison technique. DNA testing, on the other hand, relies on quantifying genetic information extracted from cells. (Hair itself is not a source of DNA for forensic analysis: The cells at the root must be present along with the hair for a usable profile to be extracted.) When it comes to the conclusive identification of individuals, DNA testing is key.
Of all the physical evidence found at crime scenes, hair is one of the most common, thanks to the fact that the average person can lose anywhere from 50 to 100 hairs over the course of the day. Technicians will recover as much hair as possible at a crime scene, and from there, those hairs are examined using a specialized microscope. Skip Palenik, a microscopist who specializes in hair and fiber evidence at Microtrace, describes a very different modern process than the kind used with historical microscopes.
Specialized microscopes today have a feature called an optical bridge that allows analysts to compare samples recovered from a crime scene side-by-side with known samples taken from a suspect. With such a powerful specialized microscope, the trained eyes of examiners can see the smallest details in the layers of proteins that make up human hair, minutely describing features of hair shape, color, density, and texture. They note different patterns and colors in hair, and look at physical damage that might indicate the hair’s history, such as being ripped, pulled, or burned, or naturally falling out. Under the microscope, evidence of cosmetic treatments or even louse eggs can help investigators learn about the history of a particular hair.
“A person who knows what they’re doing can make certain inferences,” Palenik explains. “What you can say in microscopy is that the two hairs can’t be distinguished from each other. That’s not the same thing as saying they came from the same person.”
DNA Is The Way
In Tribble’s trial, testimony offered a statistical probability of one in 10 million that the hairs recovered from the stocking mask belonged to Tribble. But there are no statistics of how many people in a given population have particular colors, textures, or types of hair. Multiple genes affect the color and texture of a person’s hair, which often varies not only in different people in the same family, but in different places on the same head. Some of the hair characteristics examiners look at under the microscope can change over a person’s lifetime, either by choice or by biological processes.
By contrast, a DNA profile identifies only one person, can be compared to known population statistics, and never changes. When a genetic profile is developed, it is consistent throughout one person’s life, does not vary from analyst to analyst, and relies on statistics, not visual examination.
And again and again, DNA analysis has shown that the hairs that microscopic analysts traced to a particular individual actually could not have belonged to them. Without population statistics, identifying someone by the supposedly unique, visual characteristics of their hair is impossible.
But for many, including Santae Tribble, the truth came too late. After his release, he joined other wrongfully incarcerated people in speaking out about their experiences and urging law enforcement and prosecutors to reconsider the way microscopic hair analysis was used in courtrooms. He passed away in June 2020 after a long illness.
The murder of John McCormick remains officially unsolved.