In 1974, a 73-year-old woman was found murdered in Torrance, California. Police quickly decided that Walter Marx, a tenant in her boarding house, was the likely suspect. There wasn’t much evidence, but the coroner had noticed an “elliptical laceration” on her nose that might have been a bite mark inflicted during a struggle. The prosecutor brought in three dentists to see if they could match the injury specifically to the suspect’s teeth. They took a mold of Marx’s mouth. Meanwhile, the victim—who had been buried six weeks earlier—was exhumed. Then the dentists went to work trying to prove a match.
Dentists had been involved in forensic work for years; they were often called in to help identify human remains using dental records. Some of these dentists were eager to get into the more glamorous (and lucrative) work of identifying perpetrators and testifying at trials. There was just one hitch: The claim that human teeth would leave a unique impression in human flesh—and that such an impression could be reliably tied to a single person—had never been demonstrated in any sort of laboratory study. In fact, there was no scientific basis for it at all. According to the Supreme Court’s “Frye test,” scientific evidence should be allowed at trial only if it is generally accepted by the “relevant scientific community.” In the Marx case, though, even the judges noted that there was “no established science of identifying persons from bite marks.” Nonetheless, the notion looked like common sense to them. The bite-mark evidence was admitted. Marx was convicted. The dentists were off to the races.
The Marx trial set a precedent: Once bite-mark evidence had been allowed in court, prosecutors began putting dentists on the stand across the nation. And bite-mark analysis was just one of many “feature-comparison” forensic methods that took off in the 1970s and ’80s. Technical evidence from crime scenes had been used in investigations and prosecutions for more than a century. (New York City set up a fingerprint bureau in 1903.) But now the field exploded, with practitioners claiming remarkable precision in matching tire-tread marks to specific cars, vague footprints to particular shoes, or stray hairs to alleged perpetrators. Ballistics, tool marks, blood-splatter analysis—we’re all familiar with these techniques because we’ve seen them used in a thousand episodes of CSI and other crime dramas.
As with bite marks, these methods were developed not to answer scientific questions but to serve the needs of prosecutors. The techniques were never tested in a laboratory. No independent groups tried to establish their accuracy. In actual science, claims are routinely challenged. The results of experiments aren’t accepted until other scientists have replicated them. But the growing cadre of “forensic scientists” had no incentive to question their colleagues’ claims or test their proficiency. Forensic experts enjoyed the esteem of their colleagues and the satisfaction of helping put bad guys in jail. Many made good livings testifying in criminal trials. A few, such as “pathologist to the stars” Michael Baden, became bona fide celebrities. Why rock the boat by demanding scientific evidence that the techniques really worked?
This doesn’t mean all forensic evidence is worthless or that forensic experts are all charlatans. But it does mean that, until recently at least, we’ve had no way of knowing how accurate a supposed match between, say, bits of fiber or a bullet and a gun barrel might be. On the stand, forensic specialists have every incentive to exaggerate their certainty and to downplay any scientific doubt or ambiguity in their findings. One of the most notorious pioneers of bite-mark analysis was once asked to specify his error rate. “Something less than my savior, Jesus Christ,” he answered.
Those boom times for forensic experts were also a boon for prosecutors, especially those whose cases were otherwise shaky. By the 1990s, thousands of suspects each year were being convicted on the strength of testimony from forensic experts.
M. Chris Fabricant, director of strategic litigation for the Innocence Project, fights to overturn flawed convictions and free prisoners who were unjustly imprisoned. Many of his cases involve bogus forensic evidence. He believes that the media’s credulous portrayal of forensic work—whether in fictional or “true-crime” stories—is part of the problem. “Jurors go into court with the expectation of two things,” he said when I recently interviewed him for a podcast. “One, that there will be scientific evidence available, and Two, that that evidence will be conclusive. And that’s just not the reality of our legal system at all.” Fabricant’s new book, Junk Science and the American Criminal Justice System, chillingly recounts case after case in which juries, awed by the supposed expertise of forensic analysts, overlooked alibis and other exonerating evidence in order to convict suspects. Some of these falsely convicted men spent decades on death row.
But then along came DNA. Unlike other forms of forensic evidence, analysis of crime-scene DNA underwent serious scientific scrutiny. Once some early problems were sorted out, it became a reliable method to connect a particular suspect to a particular crime. In the early 1990s, it also became a way to prove the innocence of the unjustly convicted. In more than 300 cases since then, the Innocence Project has been able prove the lack of guilt of its clients through the testing of old crime-scene DNA. Many of those false convictions had been based on testimony from leading experts in forensic science. In other words, this wave of DNA exonerations revealed that the supposedly rock-solid forensic evidence presented at trials was often little more than speculation—if not fraudulent.
In 2009, the National Academy of Science issued a blistering report challenging a whole gamut of forensic techniques. The report concluded that “much forensic evidence—including, for example, bitemarks and firearm and toolmark identifications—is introduced in criminal trials without any meaningful scientific validation, determination of error rates, or reliability testing to explain the limits of the discipline.” Of all the forensic methods commonly presented at trials, the NAS said, the only type of evidence that could reliably link suspects to crimes was DNA. Other studies have documented high error rates for hair analysis, techniques to identify bullets through metallurgical testing—even fingerprint identification turns out to be far less reliable than most of us imagine.
These critical studies have sparked modest reform in the forensics field, including efforts to document the scientific basis of certain techniques. But there has been a lot of pushback as well. Despite all the research casting doubt on forensic overreach, too many prosecutors just can’t quit the practice. And too many judges still allow dubious forensic evidence in their courtrooms. Bite-mark evidence, perhaps the shakiest of all forensic methods, is still admissible in all 50 states. And that’s a scandal.
Activists on the left have long been skeptical of law enforcement, and many want to roll back the extraordinary power our legal system grants prosecutors. On the other hand, most conservatives (libertarians aside) reflexively tend to trust law enforcement. Crime is a real and growing problem, after all. And dangerous criminals belong in jail. In recent years, though, the Justice Department’s dishonest campaign against Donald Trump opened conservatives’ eyes to the ways law-enforcement officials can abuse their powers. There was a faction in the FBI that was sure Trump was guilty of something, so they set out to find the crime—or invent one. Many false convictions based on junk science show a similar pattern on a smaller scale. Investigators and prosecutors find a suspect they assume is guilty, and then they rely on shoddy evidence—or manufactured evidence—to prove their case. In Fabricant’s words, they “paint a bull’s-eye around a target.”
Conservatives and liberals alike should be outraged when the state abuses its vast investigative prosecutorial powers in this way. Our justice system is built on the idea that ordinary citizens are fully capable of determining guilt or innocence. Junk forensic science is dangerous because it aims to supersede that commonsense judgement. Our forensic experts have arcane scientific knowledge, prosecutors tell juries. You lay people can’t possibly understand it, so just trust them. They’re experts, after all.
That’s not the American way. These revelations about bad forensic science should remind us never to abandon our own judgement or put all our trust in the cult of the experts. All too often, they are just making it up as they go along. And CSI is just a TV show.
Photo: Sonja Flemming/CBS ©2012 CBS Broadcasting, Inc. All Rights Reserved.
We want to hear your thoughts about this article. Click here to send a letter to the editor.
