Increasing Eyewitness Accuracy in Police Lineups
Identifying the true criminal from a lineup of suspects is a classic police technique that too often leads to inaccurate arrests and convictions. Psychological research has suggested ways to improve the accuracy and fairness of this technique.
Lining up suspects in front of a one-way mirror and allowing eyewitnesses to choose which one is the perpetrator is standard police procedure. Yet DNA evidence has repeatedly revealed the limitations of this technique: Many prison inmates whose convictions hinged on eyewitness identification were later proven innocent by DNA testing.
Long before DNA analysis was possible, psychologists doubted eyewitness accuracy in the lineup procedure. In one early experiment, psychologists Roy Malpass, PhD, and Patricia Devine, PhD, staged a crime in the middle of a lecture. A male "vandal" (who was actually hired by the researchers) entered the lecture hall, exchanged heated words with the instructor and knocked over a rack of machines. The audience was then asked to participate in a lineup to identify the vandal.
Results showed that the accuracy of the witnesses' identifications depended on the instructions the researchers gave them. The differences between the two sets of instructions were subtle: One set implied that the witness had to choose among the suspects in the lineup, while the other set implied that the witness did not have to make a choice. The researchers then included the real "criminal" in the lineup only half the time.
The researchers found that telling witnesses they didn't have to choose a suspect led to fewer false identifications — but importantly, that instruction did not hinder witnesses' ability to make accurate identifications.
Various other interactions between law enforcement officials and eyewitnesses, both before and after a lineup, can affect the witness's memory and identification as well. Research shows, for instance, that identification errors can occur when subjects view photos of suspects before picking them out of a lineup.
Psychologists have also explored the ways in which giving feedback after a lineup can distort the witness's memory. A 2014 analysis examined 23 studies involving 7,000 participants from the United States, Canada, Australia and Europe. The results showed that when a lineup administrator confirms the witness's choice, it can significantly inflate the witness's confidence in that judgment — a consequence that could affect later testimony. When post-lineup feedback suggests the witness didn't choose the right person, it reduces witness confidence, though to a lesser degree.
Other research has explored the complex role that emotion can play in the accuracy of eyewitness testimony. For instance, one study found that compared to emotionally neutral people, eyewitnesses experiencing greater negative emotions were able to provide a more complete description of the perpetrator, yet were actually less likely to correctly identify the perpetrator from a photographic lineup.
Researchers have reported that mistaken identifications are the leading cause of wrongful convictions. In a 2008 analysis of 200 convictions later overturned by DNA evidence, nearly 80 percent included at least one mistaken eyewitness. Nevertheless, eyewitness testimony is still regarded as a strong form of evidence in legal proceedings. Psychological research on this subject has both pointed out problems with relying on eyewitness evidence and suggested ways to improve its quality.
In response to research findings about faulty eyewitness testimony, then-U.S. Attorney General Janet Reno ordered the formation of a panel of experts to suggest improvements to the system. The resulting Technical Working Group for Eyewitness Evidence (TWGEYEE) established the first set of uniform practices for the collection and preservation of accurate and unbiased eyewitness evidence. These practices are outlined in the document "Eyewitness evidence: A guide for law enforcement" (PDF, 212KB) (1999).
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American Psychological Association, April 2014