DNA evidence frees the innocentl: but when we're not careful, this powerful technology can help imprison the wrongly accused.

• Author: Norris, Robert J.

SIR ALEC JEFFREYS didn't know what awaited him when he entered his lab in Leicester, England, on September 10, 1984. "My life changed on Monday morning at 9:05 a.m.," he later told an interviewer at the University of Leicester. "In science, it is unusual to have such a 'eureka' moment." But the discovery he made that day in the science of DNA would turn criminal justice on its head.

The first genetic fingerprint was discovered "purely by accident," says Jeffreys. He and his team were studying the evolution of mammalian globin genes when they discovered repetitive DNA sequences spread through the genomes of almost all the species they tested. Further examination showed that they were present in most mammals and that the patterns appeared to be different in each animal. Thinking that these might act as markers that would help pinpoint the genes responsible for particular traits, they set up an experiment to look for them in human beings.

In September 1984, the experiment revealed several markers in the human genome, which appeared to be passed down through families and unique to each individual. The team first published its findings in 1985; a second article that year concluded the probability of two individuals having the same DNA fingerprint was less than one in 33 billion. The researchers realized immediately that their discovery would have radical implication for at least two areas: criminal investigations and paternity cases.

DNA evidence quickly found its way into American courtrooms, but the technology wasn't always used responsibly. It was soon challenged in court, a charge led by defense attorneys Barry Scheck and Peter Neufeld. The pair went on to found the Innocence Project, which is most famous for using DNA evidence to exonerate 350 people who were convicted of crimes they didn't commit. Their challenges to the early use of DNA fingerprinting in criminal trials encouraged labs to be more modest and precise in their claims, but it also sowed seeds of doubt about the accuracy of the techniques, and about the criminal justice system more broadly.

THE FIRST CRIMINAL CASE

IN NOVEMBER 1983, the body of 15-year-old Lydia Mann was found in the village of Narborough, England. She had been raped and strangled. The crime sparked a major investigation but went unsolved. Three years later, in July 1986, a similar crime occurred in the neighboring village of Enderby, where another 15-year-old, Dawn Ashworth, was found beaten, raped, and strangled. This time investigators had a suspect: Richard Buckland, a 17-year-old who worked in the kitchen of a local mental hospital.

Buckland had a very low I.Q. Upon questioning, he confessed to Ashworth's murder but not to Mann's. So investigators asked Jeff reys--who was in the spotlight after helping settle a paternity dispute in a high-profile immigration case the previous year--to compare Buckland's DNA with a sample taken from the Mann crime scene, which he did in September 1986.

The results showed that the samples did not match. Surprised and unsure how to proceed, police asked Jeffreys to test Buckland's sample against material from the Ashworth investigation, the crime to which he had confessed. The tests showed that the two crime-scene samples matched each other, but neither one matched Buckland, shocking not only the police but also Jeffreys, who found the result "blood-chilling." After the Home Office's Forensic Science Services confirmed the results, all charges were dropped against Buckland. Thus, Jeffreys said, "the first time DNA profiling was used in criminology, it was to prove innocence." It would later help identify the real killer, Colin Pitchfork.

THE DNA INDUSTRY

JEFFREYS AND HIS team were soon inundated with requests for assistance. Jeffreys described this time as "simply insane." In response to the incredible demand, Imperial Chemical Industries (ICI), the largest chemical company in the United Kingdom, opened its first DNA testing laboratory in the summer of 1987.

ICI Americas started offering DNA tests in the United States in October 1987 as Cellmark Diagnostics USA. Although the company initially planned to focus on paternity testing, it soon began accepting forensic casework. Concerned about the stricter admissibility standards in U.S. courtrooms, Cellmark hired a former chief of the Bureau of Alcohol, Tobacco, and Firearms' forensic laboratory, Daniel Garner, who immediately began preparing the company to introduce its tests into court, hiring scientists and building a network of expert advisers to shore up the scientific and technical side of things.

Cellmark also began to connect with criminal justice professionals through direct mail campaigns, advertisements in legal publications, and presentations at professional meetings. It presented its DNA fingerprinting technology as a definitive way to link offenders to a crime scene. In one 1988 advertisement, for instance, the company claimed that "criminals leave more conclusive evidence than ever before" and that DNA fingerprinting "may be the difference between...