For the last 15 years, crime investigators have employed a type of sophisticated DNA testing to determine the source of genetic material,like a hair or skin, recovered at a crime scene.
That testing is the most accurate way to analyse material from a crime scene — especially small or damaged samples.
Despite the availability of this DNA testing, however, the FBI recently revealed that some jurisdictions around the US are still relying on an outdated technique called hair microscopy.
Hair microscopy — which uses a microscope to compare two different hair samples — is cheaper than DNA testing, but a 2009 report in the National Academy of Sciences called the technique “highly unreliable.”
“When it comes down to it, it’s one human being eyeballing one hair compared to another hair,” Lindsay Herf, post-conviction project counsel at the National Association of Criminal Defence Lawyers (NACDL), told Business Insider.
Problems with hair microscopy
As such, the technique is prone to human error. While conducting a review of former cases, the FBI recently dropped the bombshell that most of the experts in a major forensic unit dedicated to hair microscopy gave flawed testimony during a 25-year period, potentially affecting more than 3,000 defendants. Thirty-three inmates currently on death row were also convicted using the technique.
About 74 out of 329, or 22%, of DNA exonerations have involved faulty microscopic hair analysis, Paul Cates, communications director of the Innocence Project, told Business Insider.
In one particularly egregious case, two FBI forensic experts confused a human hair with a dog hair. The defendant in that case, a man named Santae Tribble (pictured above), served 28 years in prison before DNA evidence exonerated him, according to the Innocence Project
Examining this cat hair and dog hair (courtesy of the North Carolina School of Science and Mathematics) gives a sense of the problems present in hair microscopy. A lab technician would have to visually compare similar hair samples like these and determine whether they matched hair found at a crime scene.
While the “eyeballing technique” is already subjective, additional problems exist. For example, no national standards exist for what constitutes a “match” between two samples, Herf says.
One expert might find 18 similarities between hair found at the scene and the suspect’s while another might require 24 before calling the two samples a “match.”
This subjectivity leads to three basic types of errors in cases, according to Herf:
- Error Type 1: An analyst erroneously determines the hair matches a specific person and no one else.
- Error Type 2: The analyst might give a statistical probability that the hair came from a specific person when, in fact, there’s no way to quantify that likelihood. “This leads the jury to believe that a particular statistic can be assigned to hair microscopy,” Herf explained. “But rather, it’s a pool of unknown size.”
- Error Type 3: Analysts might cite their experience as a way to convince the jury by making a comment like: “Over the last 12 years, … I’ve only had two occasions out of the 10,000 people where I had hairs from two different people that I could not separate them.” Since hair microscopy doesn’t have a strong scientific basis, the expert’s experience shouldn’t necessarily serve as a way to bolster his or her opinion.
DNA testing as a proven alternative
Unlike hair microscopy, mitochondrial DNA testing uses objective scientific analysis. Since mitochondria is inherited maternally, siblings would share identical mitochondrial DNA, providing more opportunities to find a match.
“Mitochondrial DNA analysis looks at the genetic makeup of the hair and the type, and the DNA profile that comes from the sample would be exactly the same as that of the person who would be the donor of the hair,” Dr. Terry Melton, founder and former laboratory director of Mitotyping Technologies, told Business Insider.
“Instead of looking at something subjectively [like hair microscopy does], you have actual data.”
DNA testing also has to meet national standards, set by the FBI and other accreditation groups.
“It’s very uniform across all labs, across the country and even across all countries,” Melton said. “It’s the same no matter who examines.”
DNA testing is pricey, though. Because the risk of contaminating samples is high, labs must follow specific guidelines when conducting DNA tests, which requires a lot of manpower.
“When a single hair is tested, it’s the only thing the laboratory technician is doing for two to three days,” Melton explained.
Despite the challenges, Melton said a case that relies on only microscopy should never go to trial. While federal law authorities the FBI to maintain a national DNA database, none exist that require DNA testing in criminal cases. Grants do, however, assist state and local jurisdictions with the costs of forensic testing.
“That’s not acceptable. Every case that goes to court should have DNA testing as well,” Melton said. “There’s no law that says [a prosecutor] has to do that … but the defence should challenge that. An informed attorney, group, judges, and so forth, would know better.”
Unfortunately, the problem doesn’t stop at hair microscopy. Other “eye-balling techniques” for determining evidence still exist — such as bite marks, ballistics, and even fingerprints.
“This is a mass disaster, but it is one that judges have been largely indifferent to and lawyers have had halting success in revisiting,” Brandon L. Garrett, professor of law at the University of Virginia and author of “Convicting the Innocent,” told Business Insider via email.
As of March 2015, the FBI had reviewed about 500 of the 3,000 cases involving hair microscopy.
While the FBI noted that “some jurisdictions” continue using hair microscopy when they deem DNA testing to be too expensive, the federal government has stopped making that mistake. Mitochondrial DNA testing on hair has been routine at the agency since 2000.
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