Troy Davis: Victim of Eyewitness Testimony

Troy Davis is scheduled to be executed today, charged with murdering a Savannah police officer in 1989. Davis’ execution has been scheduled 4 times, and appealed again and again. The most recent appeal to halt the lethal injection was rejected yesterday and it seems Davis’ attorneys are out of options. The death penalty is a controversial issue in and of itself, but some of you may wonder why people are up in arms over the execution of a convicted murderer? Well, those protesting the execution have a right to be concerned and it has everything to do with the evidence used to convict him.

You can read the details of the arrest, trial, and conviction all over the internet (I checked on Wikipedia and Amnesty International), but the short version is that Davis was accused of shooting one man, assaulting a homeless man with a pistol, and killing a police officer, and the case against him is built entirely on eyewitness testimony. In fact, the only physical evidence collected from the scene were some bullets and shell casings (no DNA or fingerprints), and all but 2 of the witnesses have since altered their testimony, citing police coercion in accusing Davis. Nine of those individuals have implicated the principle alternative suspect, Sylvester Coles. You may be thinking to yourself, “If so many people supposedly saw him do it, how could they change their minds now? Isn’t eyewitness identification important in a murder conviction?” The answer is yes, eyewitness testimony is important, but it is dangerous to rely on as a sole source of evidence.

Consider the case of Ronald Cotton. In 1984 a young woman named Jennifer Thompson was raped by a man who broke into her home in the middle of the night. During her attack, Thompson actively tried to study her assailant’s face, hoping to identify the man to police if she were to survive. Months later, she picked Ronald Cotton out of a police lineup, testified twice against him, and Cotton was sentenced to life plus 54 years. However, after serving 10.5 years in prison, Cotton was exonerated on the basis of DNA evidence and the actual rapist, Bobby Poole, was convicted of the crime. Thompson had purposefully studied attacker’s face – how could she have identified the wrong man?

One source of her mistake may have been the type of police lineup she saw. In a simultaneous lineup, the suspect and several foils are presented to the witness at the same time, whereas in a sequential lineup they are presented one at a time. Simultaneous lineups tend to result in more identifications than sequential lineups, but a greater proportion of those are false alarms than in the sequential format. The reason for this phenomenon is that simultaneous lineups allow witnesses to make relative judgments (i.e. choose the person who most resembles the culprit) while sequential lineups force the witness to make an absolute judgment about each person (i.e. is this person the culprit or not?). False identifications are never made on purpose, but the format of the lineup can influence what kind of decision-making strategy the witness will use.

Another source of false alarms is the quality of the foils. In order for the lineup to be fair, the foils must look sufficiently similar to the suspect that witness cannot rely on unique features to make the identification. If the witness reports that the culprit was wearing glasses and the suspect is the only person in the lineup with glasses, then lineup would not be considered fair. A better lineup would include several foils who also wear glasses so that the witness could not rely on only that feature. Otherwise, police could pick anyone who matches the description and create a lineup of unfair foils that would guarantee that their suspect would be identified, innocent or not.

Witnesses can also be influenced by the instructions given to them. For example, if told to “pick the gunman out of the lineup” then the witness is led to believe that the gunman is actually present – even though he may not be! Crime shows are particularly negligent about acknowledging that suspects are only suspects and they may not have found the true culprit. This kind of subtle suggestion is called misinformation and can even alter a witness’s memory of an event. In one study, participants viewed a video of a car accident and, one week later, made wildly different speed estimates depending on whether the experimenter used the verb “hit”, “contacted”, or “smashed” when asking how fast the car was going. Some participants even answered that they had seen broken glass when there was none in the video! Unlike primetime television dramas, real policemen are much more careful about avoiding misinformation when giving instructions and asking questions.

In Davis’ case, it seems that some witnesses may have been affected by straight up coercion rather than misinformation or lineup procedures. The fact that witnesses have changed their testimony indicates that they were not merely mistaken about the shooter’s identity but felt compelled to implicate him for other reasons. The American justice system is founded on some revolutionary principles that were designed to protect the innocent, but those principles are only as good as the people who enforce them. I personally believe that Davis is wrongfully accused and innocent man will be executed this afternoon.

If you want to learn more about eyewitness testimony, you can visit The Innocence Project to read more about the surprising number of cases of conviction via misidentification. And if you want to do something to support Troy Davis, visit Amnesty International to find out how.

Update 9/27/11
NPR just published an excellent article that examines the debate over using eyewitness testimony to convict suspects in death penalty cases. They cover many of the ideas I have mentioned above, in addition to the notion that witnesses’ memories of an emotional event – such as a police shooting – can change drastically over time even while their confidence in their testimony remains very high. To learn more about this phenomenon, check out this Psychology in Action post about flashbulb memories.