Lineup instructions to the witness are very important. In a study by Roy Malpass and Patricia Devine, students saw a staged act of vandalism, after which they attended a lineup. Half of the students received “biased” instructions: They were led to believe that the culprit was in the lineup. The others were told that he might or might not be present. Lineups were then presented either with or without the culprit. When the students received biased instructions, they felt com- pelled to identify someone and often picked an innocent person
Additional studies have both confirmed and qualified this basic result: When the criminal is present in the lineup, biased instructions do not pose a problem. When the criminal is not in the lineup, however—which occurs whenever the police suspect is truly innocent—biased instructions substantially increase the rate of mistaken identifications. Again, the story of Steve Titus is a case in point. The police told the victim to pick her assailant from a group of six. After studying the pictures for several minutes and shaking her head in confusion, she was urged to concentrate and make a choice. “This one is the closest,” she said. “It has to be this one”.