Interrogating to detect deception and truth : effects of strategic use of evidence

Sammanfattning: Several decades of research has shown that people are poor at detecting deception. This thesis, based on four empirical studies, aimed at exploring human deception detection accuracy in the context of interrogations. In three of the studies, there was a special focus on the presence of evidence in the interrogation, and how strategic use of this evidence affected the statements of the suspects as well as the accuracy of the lie-catchers. In previous research, the fact that there in real-life situations often exists evidence against a suspect has been neglected. It was expected that it would be beneficial for deception detection to withhold the evidence during the interrogation, and that this would lead to liars contradicting the incriminating information to a higher degree compared to truth tellers. Differences in statement-evidence consistency between liars and truth tellers could then serve as a cue leading to more accurate veracity judgments. In Study I, experienced police officers (N = 30) were set free to conduct interrogations with mock suspects in the manner of their own choice. They also watched a video-taped interrogation conducted by one of their colleagues. Both when interrogating and observing video, the police officers achieved deception detection accuracy levels (56.7%) similar to the level of chance. The aim of Study II was to examine the effects of disclosing the evidence at different stages of the interrogation. It was expected that disclosing the evidence late (vs. early) in the interrogation would provide a better basis for correct veracity judgments. The reason for this was that late disclosure of evidence would make liars and truth tellers differ in terms of statement-evidence consistency. Mock suspects (N = 58) were interrogated by experimenters. Lie-catchers (N = 116) who watched late disclosure interrogations (accuracy 61.7%) significantly outperformed those who watched early disclosure interrogations (accuracy 42.9%). In Study III, police trainees (N = 82) either were or were not trained in strategically using the evidence when interrogating lying or truth telling mock suspects (N = 82). Liars interrogated by trained interrogators were more inconsistent with the evidence compared to liars interrogated by untrained interrogators. Trained interrogators obtained a considerably higher accuracy rate (85.4%) than untrained interrogators (56.1%). In Study IV, the strategies reported by the suspects (N = 82) in Study III were examined. Guilty suspects, to a higher degree than innocent suspects, applied conscious strategies in order to appear truthful. Guilty suspects reported diverse strategies (such as to provide a consistent story or an alibi), while innocent suspects reported the strategy to tell the truth like it had happened, indicating a belief in the visibility of innocence (i.e., they thought that innocence shows). The results of the thesis show that when the evidence is not used strategically during an interrogation, deception detection accuracy is poor. However, when the evidence is used strategically, liars and truth tellers resort to different strategies, resulting in differences in statement-evidence consistency. This objective cue to deception provides a good basis for judging a suspect?s veracity.