Test Applied to DNA Isn’t Always A-OK

It’s the stuff of TV dramas: A horrible crime is committed. Police scour the scene, collecting microscopic bits of genetic material from blood, strands of hair, droplets of saliva. A DNA profile is generated. It’s compared with the suspect’s profile. They match, and the suspect goes to prison.

Case closed. Go to commercial.

DNA evidence has been acclaimed as the magic bullet of crime fighters for nearly two decades. Along the way, William Thompson has become one of its principle skeptics, questioning its infallibility by studying the poor marksmanship that can result when forensic technicians pull the trigger.

“I wouldn’t call myself a critic of DNA evidence,” said Thompson, a UC Irvine professor of criminology, law and society who is one of the nation’s leading experts in the field. “I think DNA evidence is great. I’m a critic of bad DNA evidence.”

Thompson’s review last year of Houston’s crime lab led to its closure and a reconsideration of a decade’s worth of criminal convictions that were based on DNA matches from the lab.

In March, a 21-year-old Texas man serving a 25-year sentence for a 1998 rape was released from prison after Thompson’s review of DNA evidence in the case. Prosecutors argued at trial that Josiah Sutton’s DNA was a 1-in-694,000 match with the rapist’s. It took a jury just two hours to convict him. In fact, Thompson was able to show that Sutton’s DNA wasn’t found in any of the police samples.

None of this surprised Thompson, an attorney who also has a doctoral degree in psychology.

Although cases of innocent people falsely convicted by bad DNA evidence are rare, Thompson sees ambiguous results, sloppy lab work or overstated findings in a quarter of the cases he examines.

The problem, he says, lies in human error and the biases of forensic scientists who work for police agencies.

“I think it’s a service industry for law enforcement,” he said. “They provide a service to clients, and the clients are law enforcement. Because of that, the culture that develops in police labs is inconsistent with upholding the best scientific values.”

That rough critique has earned Thompson praise from an unusual quarter: the Assn. of Forensic DNA Analysts and Administrators.

“I think he’s excellent, although some feel that he’s a lot more rambunctious than most defense attorneys,” said association Chairman Ron Rubocki, a forensic scientist at the University of Nebraska Medical Center.

Rubocki agrees that the public’s respect for -- and the lack of knowledge of -- science has given DNA evidence an aura of infallibility it doesn’t deserve. He also agrees that “when working for a police agency, one might be under more pressure [to make a match] and may not be as neutral as you should be.”

Thompson’s interest in forensic science dates to the early 1980s, when he studied how juries interpret statistical and scientific evidence. When DNA testing hit the scene a few years later, Thompson first planned to study how to effectively convey such evidence to juries.

But as the purported reliability of DNA matches quickly went “from 1 in 100 to 1 in 30 billion,” Thompson said, he became skeptical. His first article on the subject, co-written with a biochemist and published in 1988, noted the promise of DNA evidence but cautioned that police labs needed to adopt the scientific rigor that research in academic labs employ.

“We were inundated by defense lawyers. My phone was ringing off the hook,” Thompson said. “But the people in the forensic science community were saying ... ‘Why don’t you shut up? This is bad for law enforcement -- and good for criminals.’ ”

Over the years, Thompson has become a consultant and co-counsel on cases involving DNA evidence. He was part of O.J. Simpson’s defense team at his murder trial. He gets a couple of letters a week from inmates who see him as their last hope. He passes the ones he thinks have merit to attorneys working for “innocence projects” nationwide.

Thompson said it’s not just juries who have been led to believe that DNA evidence “is the best thing since sliced bread.” Defense attorneys unfamiliar with the pitfalls of the science are just as likely to fold -- and seek a plea bargain for their client -- when presented with a positive DNA match.

The myth of infallibility is strong. How the science is portrayed in the media -- particularly in the popular “Crime Scene Investigation” television dramas -- doesn’t help.

“ ‘CSI’ is pernicious,” Thompson said. “They portray the cowboy attitude of forensic scientists, with them busting down doors and interrogating suspects. It makes it hard to challenge bad DNA evidence.”