Lineups (Dan Reisberg, ch. 11)

There are now more than 150 cases of DNA exoneration in the United States-cases in which DNA evidence, available only after a trial was over, has shown incontrovertibly that the courts had convicted the wrong person. In each case, someone totally innocent spent years in jail, while the actually guilty person walked around free. In many cases, the innocent person, now exonerated, had been on death row, awaiting execution. If the DNA evidence hadn't been available, the wrong person would have been executed.

What produced these tragic errors? In the vast majority of cases, the mistaken conviction can be traced to bad eyewitness evidence: The juries had (understandably) been persuaded when an eyewitness confidently pointed to the defendant and said, "That's the man who raped me" (or "robbed me" or "shot my friend"). But in case after case, the witnesses were wrong, and the jury's decision was correspondingly mistaken.

It's crucial, therefore, that we ask what we can do to avoid these bad ID's, and we can be guided here by what we know about memory's operation in general, and what we know about memory for faces in particular. Some of the relevant research has identified factors that indicate when an ID is dubious, and needs to be treated with caution. In earlier Supplementary Essays, we have mentioned, for example, that eyewitness identifications tend to be less accurate when the witness and the perpetrator are of different races, or when a weapon is on the scene. This research can obviously help the courts to make better use of eyewitness evidence.

Other research has asked what steps we can take to diminish the chance of eyewitness error. For example, psychologists have offered advice on how a police lineup should be constructed-that is, what faces should be included, in addition to the suspect's-to minimize the chance of error. Evidence makes it clear that a well-chosen lineup can markedly decrease the chance of witness error. Thus, for example, it is crucial that the other faces in the lineup be consistent with the witness's initial description of the perpetrator; otherwise some lineup members may not be taken seriously as real choices for the witness.

We can also change the instructions given to witnesses. It is important, for example, to remind witnesses before viewing a lineup that they are under no obligation to make a choice, and that the perpetrator's face may or may not be among those presented. This instruction is quite effective in discouraging false ID's, and so can improve accuracy.

A different proposal concerns how the faces are shown: In a standard lineup, the witness is shown all six faces at once, and must choose from among the group. In a sequential lineup, the witness is shown the faces one by one, and must make a yes or no judgment about each. This procedure, too, seems to improve accuracy, decreasing the number of false ID's.

These steps are each relatively small, but their impact on improving eyewitness accuracy can be quite large. It is therefore gratifying that law enforcement is taking these steps seriously with a real prospect that we can use what we know about face memory and eyewitness behavior to improve the criminal justice system.

To learn more about this topic in cognitive psychology and the law:

See, in the textbook chapter, pages 389-397
 
* Wells, G. L., Malpass, R. S., Lindsay, R. C. L., Fisher, R. P., Turtle, J. W., & Fulero, S. (2000). From the lab to the police station: A successful application of eyewitness research. American Psychologist, 55, 581-598.