Jennifer Thompson and Ronald Cotton have every reason to be enemies.

In 1984, an intruder broke into Thompson’s apartment and raped her. She identified Cotton as the rapist in both a photo array and a live lineup. Although Cotton proclaimed his innocence, he was arrested, tried, and convicted. The prosecution’s case rested mainly on Thompson’s identification, and during the trial she testified that she was “absolutely sure” Cotton was the man who raped her. Cotton was sentenced to life in prison plus 54 years.

But 10-and-a-half years later, things changed drastically. Cotton was exonerated based on DNA evidence that showed that a man named Bobby Poole had raped Jennifer Thompson. In a hearing that occurred after Cotton’s trial, Thompson was shown a picture of Poole. She said “I have never seen him in my life.”

You might expect Thompson would do everything possible to avoid meeting the man she had wrongfully condemned to prison. You might expect Cotton to hate the woman who took away ten years of his life. You would be wrong. Consumed by guilt when she learned her mistaken identification sent an innocent man to jail, Thompson made arrangements to meet Cotton. Ever since, they've become friends who work together to inform and educate others about the unreliability of eyewitness identification.

High profile missteps in stories like Thompson and Cotton’s contribute to the belief that eyewitness memory is unreliable and that the confidence eyewitnesses have in the accuracy of their memories is misplaced. However, a recent review of research on eyewitness memory published in the American Psychologist indicates that the situation is not as bleak as many believe. The researchers argue that the confidence an eyewitness has in their memory when they first identify a suspect in a lineup (emphasis ours) is a more reliable indicator of the actual accuracy of their memory than many realize. In fact, it’s a much more reliable indicator of accuracy than the confidence expressed by the witness during a trial.

Today, evidence from a variety of sources supports this claim that initial levels of confidence are diagnostic of guilt. And there have been many suggestions about how to make the best use of these newer research findings to reduce the number of people who are convicted of crimes they did not commit.

Looking back, Thompson was not overly confident when she first picked Cotton out of a lineup. Yet by the time the trial came, Thompson was very confident when she identified Cotton as the rapist. And in hindsight, that shouldn’t be surprising. Within the modern legal environment, there are a number of factors that can turn an initial uncertainty into a high level of confidence at trial. But if new research and its corresponding recommendations had been in place when Cotton was tried in 1985, he might not have been sent to prison.

Eyewitness memory and eyewitness confidence

Cotton is far from the only person convicted of a crime he did not commit based on mistaken eyewitness testimony. The Innocence Project reports that eyewitness misidentification was a factor in 72 percent of 325 cases in which judgments of guilt were subsequently overturned based on DNA evidence. By far, eyewitness misidentification was the most frequent contributing factor in these wrongful convictions.

Anyone familiar with the last 40 years of research on human memory in general and eyewitness memory in particular will not be surprised to hear that eyewitness identification can be unreliable. To get a sense of how malleable human memory can be, consider the difference between human and digital memory. When you take a picture with your cellphone, a more or less accurate image of what lies in front of the camera lens is stored in the phone’s memory where—barring accident—it remains unchanged and can be retrieved at will.

Human memory doesn’t work this way. Storing an event in memory, retaining that information over time, and retrieving it at a later date are all affected by a wide variety of factors that modify or distort memory for the event. The malleability of human memory is so great that people can be induced to remember and sincerely believe episodes from their past that never actually happened, such as being hospitalized for an illness or lost in a mall as a child.

Given that fragility, are there criteria we can rely on to determine whether a memory is accurate in the face of so many factors that can make memory unreliable? Well, the confidence a person has in the accuracy of their memory has been suggested as one such criterion.

Everyone has experienced the difference between being unsure if a memory is accurate and being certain they are remembering what actually happened. And anyone who has been involved in an argument with someone over a disputed memory knows how compelling that feeling of certainty can be. It’s very tempting to think that the confidence one has in the accuracy of a memory is a good indicator of how accurate the memory actually is. But this is a temptation that should be treated very carefully. The relationship between the confidence and accuracy of memories is complex, and confidence is known to be affected by a number of different factors that can increase accuracy, decrease accuracy, or have no effect on accuracy at all.

The relationship between confidence and accuracy is especially important when considering the value of eyewitness memory. Jurors are impressed by witnesses who identify a suspect with conviction and a high degree of confidence during a trial. Prosecutors know this and are unlikely to put a witness on the stand who is hesitant or unsure when they identify a suspect. As such, witnesses are routinely coached in how to testify so that witness identifications at trial are typically expressed with the high degree of confidence that jurors find compelling.

The result is what you would expect when you combine the unreliability of memory, highly confident identifications of suspects by witnesses, and a tendency by jurors to value high-confidence eyewitness testimony: eyewitness misidentification is the primary factor in the conviction of suspects who are later proved to be innocent by DNA analysis.