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One thing the prosecutor in Ferguson is right about: Eyewitness testimony can’t be trusted

St. Louis County Prosecuting Attorney Bob McCulloch, during the press conference announcing that Darren Wilson would not be charged.
St. Louis County Prosecuting Attorney Bob McCulloch, during the press conference announcing that Darren Wilson would not be charged.
(Cristina Fletes-Boutte/St. Louis Post-Dispatch/TNS via Getty Images)

In announcing that police officer Darren Wilson would not be charged for shooting Michael Brown, St. Louis County Prosecuting Attorney Bob McCulloch talked a lot about eyewitness testimony: how witnesses' accounts had changed or been inconsistent with physical evidence, and how some eventually admitted they hadn't actually seen the shooting.

When asked whether he thought these witnesses had lied, he said: "I think there are a number of witnesses in all honesty that truly believed what they said," McCullough said. "I think they truly believe that that's what they saw. But they didn't."

It's impossible to say whether, in this case, McCullough is right. But since the 1970s, psychologists have conducted studies on eyewitness testimony. And consistently, they've found it to be a shaky form of evidence.

As memory psychologist and law professor Elizabeth Loftus said in an interview with Slate, "When we remember something, we're taking bits and pieces of experience — sometimes from different times and places — and bringing it all together to construct what might feel like a recollection but is actually a construction."

Her experiments are telling. In one early study, she found that after watching a video of a car accident, witnesses who were asked "how fast were the cars going when they smashed into each other?" gave much higher speed estimates than those who were asked the same question with the word hit instead. A week later, those people were also much more likely to say they'd seen broken glass, even though none was present in the video.

In another experiment, Loftus showed participants a photo of a person's face. Then, some read an ostensibly accurate description of the person's face written by another witness that included a false detail — for instance, it said the person had a mustache when they actually didn't.

More than a third of these people then included that false information (usually with the exact same wording) in their own description of the face, and 70 percent of them "recognized" a person with that feature in a mock police lineup. Merely being asked leading questions about the feature led more than 30 percent to erroneously say the face had it.

Work by other researchers has arrived at similar conclusions. Even so-called "flashbulb memories" — particularly vivid memories of hugely important events — can be contaminated or altered.

A study of people's memories of September 11, for instance, had them record what they were doing and where they were when they heard about the attacks soon after them. Then, three years later, they were asked the same questions. Despite our unshakable confidence in emotionally charged event memories like these, just 63 percent of the participants gave consistent answers.

The consequences of flawed eyewitness testimony

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DNA evidence has overturned hundreds of convictions based on false testimony. (Shutterstock.com)

Though psychologists began to see how unreliable eyewitness testimony was during the 1970s, the criminal justice system didn't begin to take their findings into account until the late 1990s. The main reason it finally happened is that DNA evidence became available to exonerate people who'd been wrongly convicted — and an overwhelming majority of them had been done in mainly by eyewitness testimony.

Of the first 239 false convictions overturned by the Innocence Project, 73 percent had initially been convicted based primarily on the word of witnesses.

These false testimonies could be the product of all sorts of things. Just as in the experiments, our memories of crimes can be contaminated by things as subtle as the wording of a police officer or lawyer's question.

Media accounts of the event are particularly potent in contaminating our memories. "Once something gets out in the media, it’s really hard to un-ring that bell," Scott Lilienfeld, an Emory psychologist, recently told New York Magazine. "People have heard what other people have said, people have heard what other people have reported … and then their memory may be tainted, perhaps forever tainted by those recollections."

And a few other factors compound the problem. Studies show that less reliable witnesses tend to be more confident in their memories. Experiments have found that mock jurors tend to believe witnesses at a relatively high rate — whether or not they accurately relay what transpired during a mock crime they observed. This may be because jurors, surveys show, dramatically overrate the reliability of eyewitness testimony as a whole.

The importance of eyewitnesses in the Michael Brown case

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Police standing guard at the courthouse as the grand jury met to review the case against Darren Wilson. (Scott Olson / Getty Images News)

As laid out by Dara Lind and Jenée Desmond-Harris, the decision to charge Darren Wilson mainly turned on one question: did Wilson believe Michael Brown to be a threat to his life when he shot him?

Wilson's account of the event indicated that he did — and that the final two shots he fired at Brown hit the top of Brown's head because he was charging at Wilson.

Numerous witness accounts, as told to the media, make this scenario seem extremely unlikely. Despite some slight inconsistencies, they generally agree that Brown was surrendering, and had his hands in the air when he was killed.

It's tough to reconcile these contradictory accounts, and the research obviously doesn't tell us anything about which one was accurate. If anything, it tells us that all parties involved are likely to have misremembered the event — including Wilson, especially given the dubiousness of his account.

But this research could explain why McCullough — and, perhaps, the jurors — were hesitant to indict Wilson mainly on the basis of eyewitness testimony.

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