Eyewitness Testimony and Other Problematic Evidence

“He lies like an eyewitness.” It’s an old Russian saying, of uncertain provenance but enduring popularity among the defense bar. Unfortunately, there is truth to the proverb -- and the result is that too many innocent people go to jail for crimes they didn’t commit, and too many of the guilty go free.

A new report issued jointly by the U.S. Department of Justice and the International Association of Chiefs of Police shows how common wrongful convictions are and suggests ways to help prevent them. Decades of social-science research has concluded that eyewitness identifications of criminal suspects, long considered the gold standard in police work, have striking levels of error in both experiments and actual cases. About three-quarters of convictions overturned on the basis of DNA evidence involve eyewitness identifications. In more than one-third of those cases, multiple eyewitnesses identified the same innocent suspect.

Similarly, forensic science can prove faulty, informant testimony is often unreliable, and confessions are sometimes false. (More than one-quarter of those exonerated through post-conviction DNA tests had confessed to a crime.)

Some systemic injustices, such as onerous mandatory minimum sentences and “three strikes” laws that impose life sentences for petty crimes, can be undone by legislation or referendums. The habits, biases and practices that lead to wrongful convictions require more subtle adjustments.

The report offers useful guidelines. For example, to reduce the chance of witness misidentification, investigators should apply a “double-blind sequential” protocol -- that is, whether using photos or actual people, investigators should present suspects to witnesses sequentially rather than in a group. Focusing on one suspect at a time mitigates a witness’s tendency to choose the suspect whose appearance is “closest” to the image in mind. Likewise, the investigator presenting the suspects should have no knowledge of the case, the better to avoid transmitting clues -- verbal or otherwise -- to the witness.

In addition, “uniform standards for evidence collection, retention and preservation could bolster investigation practices and significantly reduce the chances of wrongful arrest, prosecution and conviction,” the report states. Law enforcement agencies should work through a checklist of protocols, much as doctors do when treating patients, to avoid investigative bias in their casework.

As evidence of wrongful convictions grows, aided by DNA technology and groups such as the Innocence Project, which contributed to the report, the need to overhaul investigative procedures has become increasingly apparent. In 2011, the New Jersey Supreme Court ruled that police procedures in the state must be upgraded to reflect research on witness misidentification and wrongful convictions.

Many state and local law enforcement agencies already employ some of the report’s recommendations, such as videotaping interviews, which is increasingly common. But a change in law enforcement culture is as necessary as individual actions. Law enforcement in the U.S. is extremely decentralized, with some 16,000 independent agencies dedicated to criminal justice.

The new investigation protocols will help police and prosecutors do their jobs better and buttress public faith in the criminal-justice system. That most human of systems will never be perfect. But by acknowledging the propensity for error and instituting procedural safeguards, American law enforcement can better protect the innocent and punish the guilty.

To contact the senior editor responsible for Bloomberg View’s editorials: David Shipley at davidshipley@bloomberg.net.