CRF Blog

The False Promise of DNA Testing

by Bill Hayes

In The False Promise of DNA Testing for the Atlantic, Matthew Shaer calls into question the reliability of many DNA tests.

Modern forensic science is in the midst of a great reckoning. Since a series of high-profile legal challenges in the 1990s increased scrutiny of forensic evidence, a range of long-standing crime-lab methods have been deflated or outright debunked. Bite-mark analysis — a kind of dental fingerprinting that dates back to the Salem witch trials — is now widely considered unreliable; the “uniqueness and reproducibility” of ballistics testing has been called into question by the National Research Council. In 2004, the FBI was forced to issue an apology after it incorrectly connected an Oregon attorney named Brandon Mayfield to that spring’s train bombings in Madrid, on the basis of a “100 percent” match to partial fingerprints found on plastic bags containing detonator devices. Last year, the bureau admitted that it had reviewed testimony by its microscopic-hair-comparison analysts and found errors in at least 90 percent of the cases. A thorough investigation is now under way.

DNA typing has long been held up as the exception to the rule — an infallible technique rooted in unassailable science. Unlike most other forensic techniques, developed or commissioned by police departments, this one arose from an academic discipline, and has been studied and validated by researchers around the world. The method was pioneered by a British geneticist named Alec Jeffreys, who stumbled onto it in the autumn of 1984, in the course of his research on genetic sequencing, and soon put it to use in the field, helping police crack a pair of previously unsolved murders in the British Midlands. That case, and Jeffreys’s invention, made front-page news around the globe. “It was said that Dr. Alec Jeffreys had done a disservice to crime writers the world over, whose stories often center around doubtful identity and uncertain parentage,” the former detective Joseph Wambaugh wrote in The Blooding, his book on the Midlands murders.

A new era of forensics was being ushered in, one based not on intrinsically imperfect intuition or inherently subjective techniques that seemed like science, but on human genetics. Several private companies in the U.S. and the U.K., sensing a commercial opportunity, opened their own forensic-DNA labs. “Conclusive results in only one test!” read an advertisement for Cellmark Diagnostics, one of the first companies to market DNA-typing technology stateside. “That’s all it takes.”

As Jay Aronson, a professor at Carnegie Mellon University, notes in Genetic Witness, his history of what came to be known as the “DNA wars,” the technology’s introduction to the American legal system was by no means smooth. Defense attorneys protested that DNA typing did not pass the Frye Test, a legal standard that requires scientific evidence to have earned widespread acceptance in its field; many prominent academics complained that testing firms were not being adequately transparent about their techniques. And in 1995, during the murder trial of O. J. Simpson, members of his so-called Dream Team famously used the specter of DNA-sample contamination — at the point of collection, and in the crime lab — to invalidate evidence linking Simpson to the crimes.

But gradually, testing standards improved. Crime labs pledged a new degree of thoroughness and discipline, with added training for their employees. Analysts got better at guarding against contamination. Extraction techniques were refined. The FBI created its codis database for storing DNA profiles of convicted criminals and arrestees, along with an accreditation process for contributing laboratories, in an attempt to standardize how samples were collected and stored. “There was a sense,” Aronson told me recently, “that the issues raised in the DNA wars had been satisfactorily addressed. And a lot of people were ready to move on.”

Among them were Dream Team members Barry Scheck and Peter Neufeld, who had founded the Innocence Project in 1992. Now convinced that DNA analysis, provided the evidence was collected cleanly, could expose the racism and prejudice endemic to the criminal-justice system, the two attorneys set about applying it to dozens of questionable felony convictions. They have since won 178 exonerations using DNA testing; in the majority of the cases, the wrongfully convicted were black. “Defense lawyers sleep. Prosecutors lie. DNA testing is to justice what the telescope is for the stars … a way to see things as they really are,” Scheck and Neufeld wrote in a 2000 book, Actual Innocence, co-authored by the journalist Jim Dwyer.

While helping to overturn wrongful convictions, DNA was also becoming more integral to establishing guilt. The number of state and local crime labs started to multiply, as did the number of cases involving DNA evidence. In 2000, the year after Sutton was convicted, the FBI’s database contained fewer than 500,000 DNA profiles, and had aided in some 1,600 criminal investigations in its first two years of existence. The database has since grown to include more than 15 million profiles, which contributed to tens of thousands of investigations last year alone. [more]