Living World / Genetics

All photography by Tony Law

On August 26, 1999, Sarah Hovis, a senior at the University of Virginia business school, was raped at gunpoint in her off-campus home. "I was blindfolded the whole time, and I never would have been able to pick him out of a lineup," Hovis says. Traces of the intruder's DNA turned up on the bedsheets and in the saliva he left on a beer can, but the sample didn't match the genetic material of any of the suspects. The next step was to check for leads in the state's DNA database. But Virginia had only recently begun developing DNA profiles from roughly 160,000 biological samples collected from convicted offenders. At first, no match emerged.

Then, on October 5, 1999, a call came from the Virginia lab: "We've got your rapist." Captain J. E. "Chip" Harding savors the memory. "It was probably the most exciting moment in my whole period of law enforcement." Harding had helped found a group that successfully lobbied for funds to analyze the state's backlogged samples.

The rapist was snared by what law enforcement officials call a cold hit—a random match of DNA from a crime scene and a database. Since Virginia launched the first forensic DNA database in 1989, it has notched more than 3,000 cold hits that linked otherwise unknown suspects to crimes. The matches have helped solve not only decades-old homicides but also some ongoing serial rapes, showing that forensic DNA databases aid in crime prevention as well as crime solving.

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Evidence that pins down a suspect's presence with scientific precision is a crime fighter's dream. "There's nothing more pure an identifier than DNA," says Paul Ferrara, director of the Virginia Department of Forensic Science and founder of the country's oldest state DNA crime lab. Molecular xeroxing of DNA through the polymerase chain reaction, or PCR, allows scientists to analyze DNA from the few cells a burglar sheds on the lip of a beer can, on the inside of a discarded ski mask, or on a good day (for the scientist), even the thief's smeared fingerprint. "It allows you to solve crimes in ways you'd never have been able to solve them before," says Sarah Hart, former director of the National Institute of Justice, the research and development branch of the Department of Justice.

Today all 50 states, the Army, and the FBI contribute to the Combined DNA Index System, or CODIS, a nationwide database that has tallied more than 22,000 cold hits. More than 3 million people already have their DNA profiles stored in the system. "I can easily see the current system having 50 million samples in the very near future," says Dwight Adams, the director of the massive new FBI laboratory on the Marine Corps base in Quantico, Virginia.

Although most tissue samples can be processed at the Bode lab within 24 hours, extracting DNA from highly degraded tissue can take up to two weeks.

That runaway growth may come at a serious cost, says Tania Simoncelli, a science and technology fellow with the American Civil Liberties Union. She is concerned that more and more people are being required to provide DNA samples to what can no longer be called a strictly criminal database. In January 2006, President Bush signed a law containing last-minute provisions that escaped much public notice. The provisions expand the collection of DNA samples beyond convicts to include federal arrestees as well as non-American detainees like suspected illegal immigrants or captives in the war on terrorism. "We should feel very uncomfortable now with this expansion to arrestees because we've crossed a line to innocent people," Simoncelli says.

She also worries that samples of biological material, if kept on file indefinitely, will one day be used routinely for other purposes. "The problem with storing DNA is that it's not like a fingerprint," she says. "It has the potential to provide information well beyond identification." Some law enforcement agencies are already using a technique that mines DNA for evidence of racial makeup.

And then there are problems where people might least expect them: in the lab itself. Last year the Virginia Department of Forensic Science was put under the microscope. An independent audit found that top DNA scientist Jeffrey D. Ban had erred in his interpretation of DNA results from an unusual, high-profile case. In 2000 he was asked to run modern DNA tests on 18-year-old evidence to see if the results might exonerate a convicted death row offender. The auditors found that the scientist had deviated from established procedure. Ban could not extract an adequate amount of DNA from the sample, so he increased the number of polymerase chain reaction DNA-copying rounds to try to increase the chance of obtaining usable profiles. The results were inconclusive, but Ban reported that they ruled out a new suspect whose DNA, according to a second test in 2004, proved to be part of the mix.

During a costly and time-consuming independent review of the laboratory's work in 123 other cases, reviewers detected a single inaccurate interpretation made in one case but no systemic errors or protocol deviations occurring in the lab. Ferrara reinstated Ban, who had been relieved of some duties during the review period.

Ferrara refers to the episode as a "tempest in a teapot, contrived to try to shake public confidence" in DNA laboratories. But the Virginia case created a stir precisely because the public has so much confidence in DNA evidence—so much that it's often viewed as infallible, says William C. Thompson, a professor of criminology, law, and society at the University of California at Irvine. Thompson believes that DNA databases are expanding so quickly that the public hasn't had a chance to digest the potential implications. "We need to have a national discussion about benefits and detriments," Thompson says. "People need to realize that it's possible to have errors in DNA testing that falsely incriminate people, and in fact it's already happened, and it's happened more often than we had imagined."

These vials contain samples of demineralized bone from victims of the attack on the World Trade Center. DNA will be extracted from the bone.

"Human beings make errors," says Thompson, who was part of the defense team in the O. J. Simpson trial and has become—depending on your perspective—either a reasonable voice of caution about the use of DNA samples or a thorn in the side of forensics labs. In 2002 reporter David Raziq, from Houston TV station KHOU, called Thompson to help investigate the Houston police department's forensic lab. Raziq had become suspicious when the Harris County district attorney ordered the disposal of DNA evidence in advance of a new state law allowing prisoners to petition for state-funded retests of forensic evidence. Thompson's review of the testing results led to the shutdown of the lab, the removal of hundreds of DNA profiles from the national database, and the independent retesting of DNA samples, including evidence related to several death row cases. Retesting freed Josiah Sutton, who was jailed as a teenager for rape based on a Houston lab mistake; during his original trial, Sutton had requested, but did not receive, independent DNA testing of the prosecution's evidence.

"Houston was just the Titanic of DNA labs," Thompson says. "They were doing ridiculously bad work. But that problem was not discovered by anybody in the criminal justice system because no one ever looked past the laboratory report."

As a contributor to CODIS, the lab was required to follow FBI quality assurance standards and undergo an external audit at least every two years. But it was not accredited, nor was it required to be. Although a 2004 law mandated accreditation for laboratories developing DNA profiles for CODIS, the rule does not take effect until 2007. The FBI refused to provide statistics on the proportion of profiles in the national index supplied by unaccredited laboratories.