The case against evidence

From fingerprints to high-tech CSI, forensic science plays a much smaller role than you would think

At criminal trials, there is always talk about doubt, reasonable doubt. But in recent years, with the rise of DNA technology and other forensic evidence techniques, many Americans have a growing sense of confidence, if not certainty, that we’re locking up the guilty and freeing the innocent. The backbone of modern justice, it seems, is not a judge in a long, black robe, presiding over a courtroom, but a forensic analyst in a crisp, white coat, laboring over a microscope. In science we trust.

A 2006 survey of more than 1,000 Michigan jurors found that nearly half of the jurors expected to see some sort of scientific evidence in every criminal trial. Nearly 75 percent expected to see scientific evidence presented in murder trials. And still another study, published just this year, found that people trusted such evidence almost blindly. In this study, a random sample of 1,201 potential jurors in California said they considered scientific evidence, like DNA and fingerprints, to be far more reliable than the testimony of police officers, eyewitnesses, or even the victims themselves.

Prosecutors call it the CSI effect, suggesting that fictional television shows, like the long-running “CSI,” helped convince science-wary Americans to believe in the power of forensics. But the facts haven’t hurt, either. At trial, when possible, prosecutors are always keen on

calling forensic experts to testify — even when no forensic evidence has been found. Failure to do so, prosecutors say, would almost surely sink their chances of winning a conviction.

But does forensic evidence really matter as much as we believe? New research suggests no, arguing that we have overrated the role that it plays in the arrest and prosecution of American criminals.

A study, reviewing 400 murder cases in five jurisdictions, found that the presence of forensic evidence had very little impact on whether an arrest would be made, charges would be filed, or a conviction would be handed down in court.

A mere 13.5 percent of the murder cases reviewed actually had physical evidence that linked the suspect to the crime scene or victim. The conviction rate in those cases was only slightly higher than the rate among all other cases in the sample. And for the most part, the hard, scientific evidence celebrated by crime dramas simply did not surface. According to the research, investigators found some kind of biological evidence 38 percent of the time, latent fingerprints 28 percent of the time, and DNA in just 4.5 percent of homicides.

“Forensics had no bearing on the outcome at all,” said Ira Sommers, professor of criminal justice at California State University, Los Angeles, who coauthored the research with colleague and fellow professor Deborah Baskin. “It was not a significant predictor of the district attorney charging the case and had no relation to actually getting a conviction. That’s a pretty stunning finding considering all the hype around forensic evidence.”

And according to Baskin and Sommers, there’s reason to believe that the findings aren’t limited to murder cases alone. In research yet to be published, the California professors say they have made similar conclusions regarding the small role that forensic evidence plays in solving other crimes as well. In assault, robbery, and burglary cases, investigators collect forensic evidence less than a third of the time, the researchers have found, and only a small fraction of that evidence ever gets submitted to a lab for study, making it essentially “a nonfactor,” Sommers said, “a rare phenomenon.”

The new research, to be published in the Journal of Criminal Justice, comes at a time when forensic science is already under siege, with some questioning whether certain forensic practices are even that scientific. The National Academy of Sciences authored a report last year questioning the reliability of many forensic methods, deploring the lack of standardization and certification within the trade, and calling for sweeping reforms. The report, which gave voice to concerns that many forensic scientists had been whispering for years, reached the White House, where President Obama directed a subcommittee on forensic science to study the suddenly prickly matter.

That committee is expected to report its findings and make policy suggestions in the coming weeks. Meanwhile, twice in the last 18 months, the Senate Judiciary Committee has held hearings generally bemoaning the state of American forensic science — and perhaps with good reason.

Hundreds of crime labs across the country are unaccredited; laws in most states don’t require them to be. And even those with accreditation have had problems. In 2008, the city of Detroit shuttered its crime lab after an audit found a 10 percent error rate in ballistic evidence. Last year, New York’s inspector general chastised the state police there for overlooking evidence that a crime lab analyst was fabricating data. Just last spring, San Francisco was forced to shutter its drug analysis unit after allegations that an analyst was skimming seized drugs for personal use. And Massachusetts hasn’t been immune to problems. In 2007, the state Executive Office of Public Safety commissioned a report that documented a backlog of untested DNA from 16,000 cases, including homicides and sexual assaults — a discovery that the report labeled “a crisis.”

Meanwhile, across the country, a backlog of DNA evidence continues to fester and grow despite the $330 million dedicated since 2004 to attack the mountain of untested evidence. The problem, according to a special report published in June by the National Institute of Justice, is that crime labs’ capacity for the work has not kept pace with increased demand for testing. The scientific samples just keep coming in, queuing up to be analyzed.

“I think the district attorney is just like us, just like everybody,” said Sergeant Paul McLaughlin, supervisor of one of the homicide squads at the Boston Police Department. “The more the better. The more of this stuff you can get, the more they like it.”

Police investigators first began using forensics — specifically, fingerprint identification — near the turn of the 20th century. And as late as the 1960s, such information — as valuable as it was — was stored on rudimentary cards, recalled Frank Jordan, San Francisco’s former chief of police, forcing police officers seeking an identification to wade into a sea of paper.

“You had reams and reams of files — file cards with fingerprints — and you had to check them, by hand, in our crime lab,” recalled Jordan, a 33-year veteran of the force before his retirement in 1990. “It could easily take a couple of weeks to do that. And if you were going further, and sending it on to the national lab, it would take another three to four weeks again.”

Computerization began altering that in the 1980s, Jordan said. And soon thereafter, DNA changed the entire ballgame. In 1990, a federal report determined that DNA evidence was “both reliable and valid.” Police and prosecutors quickly began seeking out such evidence, given its power to link a suspect to a crime scene — or exclude a suspect from a crime scene — through a genetic footprint.

Since 1989, according to the Innocence Project, a legal clinic dedicated to exonerating the wrongfully convicted, 261 people have been exonerated and freed from prison due to DNA evidence. And every day, in courtrooms across the country, prosecutors use such evidence to lock up the guilty.

“I can name, off the top of my head, a dozen cases that were practically solved exclusively through forensic evidence,” said Patrick Haggan, chief trial counsel for the Suffolk County district attorney’s office. “It was the main — if not the only — evidence presented to the jury.”

Undeniably, Haggan is right. Across the country, there are many examples where the discovery of DNA, or other scientific evidence, cracked a case that had long gone cold. Just last month in Suffolk Superior Court, prosecutors won a murder conviction in a case that had gone unsolved for 26 years, thanks to DNA that finally linked a career criminal to the rape and murder of an 18-year-old woman.

But Baskin and Sommers say that forensic evidence, while compelling, isn’t nearly as important to a murder case as other factors. Analyzing 400 murder cases committed in 2003 in California’s Los Angeles County, Indianapolis, and three smaller Indiana cities, the researchers found that cases were more likely to end up in court if witnesses came forward or if the victim and the suspect knew each other. Such factors made cases easier to solve and, apparently, easier to prosecute, according to the research, while, on the other hand, forensic evidence was “not a significant factor.”

“I think it’s pretty clear that forensic evidence has at best a limited impact on criminal case outcomes — at best,” Baskin said. “Really, it’s not determinant in the vast majority of cases. It does not significantly impact the conviction of cases. And I think the other point is, few cases actually have forensic evidence.”

Perhaps not surprisingly, these findings have not been met with universal applause among investigators, prosecutors, and the people actually doing the work: forensic analysts.

“You’re telling me that it doesn’t have anything to do with the prosecution?” said Pete M. Marone, who oversees Virginia’s four state crime labs and who served on the National Academy of Sciences panel that authored last year’s report on the state of American forensics. “If it’s insignificant or inconsequential, then why do my people always have to go testify why they didn’t find DNA?”

Haggan went a step further, saying the new research seemed “completely inaccurate.” He suggested that a broad overview of cases misses the subtleties within a trial and cannot account for how the mere presence of forensic evidence forces the defense to change its tactics. Take, for example, he said, the 2005 murder of cab driver Heureur Previlon in Brighton, in which police linked two suspects to the crime scene through blood found on their clothes. “By placing them at the scene,” Haggan said, “they could no longer claim they didn’t do it. They had to go with self-defense.”

However, both police and prosecutors acknowledge that there is some truth in the new findings. DNA evidence in homicide cases can be hard to come by, they acknowledge, especially in gang-related incidents, drive-by shootings, and cases where victims were randomly targeted. In Fresno, Calif., this year, police have investigated 38 murders, but found DNA in just four, according to Captain Dennis Bridges, commander of the Fresno Police Department’s violent crime bureau. And even if they had DNA evidence in more cases, Bridges added, detectives wouldn’t know that for days, maybe weeks, after the crime. What matters in the immediate aftermath of a murder, he said, is finding eyewitnesses — just as the new research concludes.

Eyewitness testimony has its own flaws; recent studies have documented deficiencies in our ability to accurately identify our attackers. But police and prosecutors agree that jurors want to hear from real people just like them, who happened to see something horrifying.

“Every case is different. But in the vast majority of extremely serious cases, you need a mix of percipient witnesses and corroboration through forensic evidence,” said Middlesex District Attorney Gerard T. Leone. “If all you have is forensic evidence — even if it’s ultra-definitive on its face; DNA matching the defendant and it’s in a critical place — jurors still want to hear from people.”

Given that reality — and the new findings — Baskin and Sommers say the lesson is clear: Police should spend more time out in the community before a homicide happens, making connections with everyday people, especially in high-crime neighborhoods, so that when a dead body turns up on a street corner, investigators have a better chance of getting witnesses to come forward.

But there’s also a secondary lesson, they say, about American society at large and the paradoxical nature of what we say we expect and what we really want. Potential jurors may say in surveys that they want scientific evidence in a criminal trial or that they find DNA evidence more reliable than the testimony of others. “But when push comes to shove,” Baskin said, “they’re still convinced by someone else testifying that they saw it.”

In this way, perhaps very little has changed about criminal trials. Perhaps modern justice isn’t so modern after all. Despite all our scientific know-how, jurors weighing life and death decisions still crave what Leone calls the “human element:” the act of watching another person testify and deciding if they’re telling the truth.

As these witnesses enter the courtroom, a hush often falls on the gallery. Jurors — bored by days of dry testimony given by well-rehearsed experts — lean forward in their seats, pens at the ready to take notes about what the eyewitness has to say. They have seen this moment on television, too, and it’s usually really, really interesting.

Freelance writer Keith O’Brien, winner of the Casey Medal for Meritorious Journalism, is a former staff writer for the Globe. E-mail him at  

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