Digging deeper: What do
  DNA exonerations teach
  us about the criminal 
  justice system?

Resources for learning more: 

The main contributors to wrongful convictions, according to the experts, are: 

The Innocence Project and a number of legal scholars have collected extensive data identifying the factors that can lead the system to convict an innocent person—and in some cases, what can be done to address those problems. 

“The exonerations of innocent people have shown that our criminal justice system is fundamentally flawed,” the Innocence Project website says. “DNA exonerations do not solve the problem—they provide scientific proof of its existence, and they illuminate the need for reform.”

What the Innocence Project has learned is surprising: 75 percent of those exonerated by DNA had been found guilty in part because they were identified as the culprit by witnesses; 36 percent were identified by more than one mistaken eyewitness. The fallibility of eyewitnesses in these cases supports decades of social science research showing that memory doesn’t work like a tape recorder—it’s malleable and easily corruptible, according to experts like eyewitness science expert Gary Wells, a psychology professor at Iowa State University. 

What's more surprising is that twenty-five percent of the 280 exonerees actually confessed to the crimes for which they were accused, made statements incriminating themselves, or plead guilty, even though DNA tests later showed they were actually innocent. According to the Innocence Project in New York, innocent people can make admissions like these under pressure in interrogation, or even plead guilty to avoid a longer sentence or the death penalty.

Still other exonerees were convicted based on botched or misrepresented forensic science, overzealous prosecutors, or overworked or in some cases sleeping defense attorneys. 

But beyond the statistics, experts have learned which practices can guard against such problems. These include taping police interviews and confessions and using double-blind identification procedures in which the officer administering a photo array or lineup doesn’t know who is suspected of the crime. These procedures, according to experts, can guard against subtle cues by police—intentional or not—that can lead to a wrongful conviction. 

The 280 exonerees are overwhelmingly people of color—disproportionately so even in an already disproportionately black and Latino population of rape and murder convicts. University of Virginia law professor Brandon Garrett studied the original trials of the first 250 DNA exonerations, and published his findings in "Convicting the Innocent: Where Criminal Prosecutions Go Wrong," Harvard Press, 2011. He says, these known DNA exonerations represent just the tip of an iceberg of innocent people in prison, and the “submerged bulk of the iceberg lurks ominously out of view.” Given that, and given the fact that experts estimate that perpetrators leave biological evidence that could be tested for DNA in only a minority of crimes, the wrongfully convicted face a real struggle to prove their innocence in a criminal justice system that values finality and sets an extremely high bar for reversing a conviction.

Here’s a short excerpt from the introduction to Garrett’s book, "Convicting the Innocent," in which he describes some of the lessons learned from studying DNA exonerations:

“In our fragmented criminal justice system, exonerations hinge on cooperation of local police, prosecutors, and judges. Most police in the 1980s did not routinely save evidence after conviction. In Dallas, Texas, where biological evidence was preserved, we have a large set of nineteen DNA exonerations. In nearby Houston, Texas, the county clerk destroyed evidence whenever its storerooms got full, so there have been just six DNA exonerations, despite a major scandal that led to the shutdown of the Houston crime lab. Further, for most crimes, there is no useful evidence collected at a crime scene that can be tested using DNA. If DNA is the “truth machine,” it tells us only about a sliver of very serious convictions, most for rape, chiefly from the 1980s. “

…[We] will never know how large the iceberg is—but we have good reasons to worry that intolerable numbers of innocent people have been convicted. A federal inquiry conducted in the mid-1990s, when police first began to send their samples for DNA testing, found that 25% of “primary suspects” were cleared by DNA before any trial.

“The trial records in these cases give us every reason to believe that most of the police, prosecutors, forensic analysts, defense lawyers, judges, and jurors acted in good faith. Few likely realized they were targeting the innocent. They may have suffered from the everyday phenomenon of cognitive bias, meaning that they unconsciously discounted evidence of innocence because it was inconsistent with their prior view of the case, or they were motivated to think of themselves as people who pursued only the guilty. That makes these cases all the more troubling. If there is no reason to think that anyone acted differently in these cases as compared to others, then similar errors may have convicted countless other innocent people and led to the guilty going free.” 

—Lindsay Markel, November 20, 2011

Last page update: November 18, 2011

© 2011-2013 Schuster Institute for Investigative Journalism at Brandeis University, Waltham, MA. All rights reserved.