forensics

Evidence on trial

On 27 February, a court ordered the District of Columbia to pay $13.2 million to Santae Tribble, who spent 28 years in prison based on bogus science. After a taxi driver was murdered in Southeast Washington in 1978, a witness had seen the killer wearing a stocking mask. In a stocking found a block away, police found a hair that matched Tribble’s “in all microscopic characteristics,” an analyst for the Federal Bureau of Investigation testified. Chances that it came from someone else were “one in 10 million,” a prosecutor told the jury. Tribble was convicted.

But a DNA analysis 31 years later showed that the 13 hairs in the stocking came from three different people, none of them Tribble, and from a dog. His incarceration wrecked Tribble’s life: The judge in this year’s decision found that it contributed to severe depression, heroin addiction, and HIV and hepatitis infections, according to The Washington Post. His story is just one of many. Forensic hair analysts have systematically overstated their evidence for decades, the Department of Justice has found, landing hundreds of innocent people in jail and some on death row.

Hair analysis is only one of many flawed forensic fields: A 2009 report from the National Research Council found that the analysis of many types of evidence—from footprints and tire tracks to bullet marks and blood splatters—lacks a solid foundation. Even DNA evidence, seen as the gold standard, can land innocent people in jail, now that new technologies can detect minuscule amounts of genetic material.

Forensic analysts are trying to do better. Many fields are testing the accuracy of existing methods and developing new ones that are more science-based. Statisticians have embarked on an ambitious effort to express the strength of so-called pattern evidence, such as fingerprints, in a more scientific way.

Meanwhile, some scientists are developing the forensic tools of tomorrow. Microbiologists are examining the possibility that the mix of bacteria living in and on the human body is so personal that it could help identify individuals. Computer scientists are helping to unmask criminals who use cryptocurrency, such as Bitcoin. Even hair has a forensic future: New analytical techniques stop short of identifying people but may provide reliable clues about a person’s origins, history, or lifestyle.

Given the history of forensics, new techniques will need to be validated more thoroughly than past methods were. And whether the methods are new or familiar, analysts, lawyers, and judges will all need to adopt a more scientific way of thinking. Bad forensic science has already wrecked too many lives.

- Martin Enserink