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Criminal investigation: Motivation, emotion and cognition in the processing of evidence

Författare Karl Ask
Datum för examination 2006-06-09
Opponent at public defense Professor, Saul Kassin, Williams College, USA
ISBN 91-628-6885-3
Förlag Göteborg University
Förlagsort Göteborg
Publiceringsår 2006
Publicerad vid Psykologiska institutionen
Språk en
Länkar hdl.handle.net/2077/676
Ämnesord Criminal investigation, motivation, emotion, Hindsight bias, police, investigate
Ämneskategorier Psykologi


This thesis examines biases in judgments made in the context of criminal investigation, drawing theoretically on frameworks developed in social and cognitive psychology. Study I investigated the existence of confirmation bias in the interpretation of criminal evidence, and the need for cognitive closure (NFC) as a potential moderator. In two experiments, criminal investigators (N = 50) and undergraduate students (N = 68) were presented with one of two alternative hypotheses regarding a homicide case, and then read the same set of evidence from the investigation. Students displayed the predicted confirmation bias, interpreting the evidence in line with their initial hypothesis. In contrast, criminal investigators made incriminating interpretations of the evidence across conditions. Investigators high (vs. low) in NFC were somewhat more likely to identify exonerating information when it confirmed their hypothesis, but somewhat less likely when the information disconfirmed their hypothesis. In Study II, the notion that non-preferred (vs. preferred) witness evidence is more thoroughly scrutinized was tested. Criminal investigators (N = 49) rated their perception of a witness who either confirmed or disconfirmed the focal hypothesis of a homicide investigation. As predicted, the hypothesis-inconsistent witness was seen as providing a less reliable statement, although its background and witnessing conditions were identical to those of the hypothesis-consistent witness. High- (vs. low-) NFC investigators were less likely to accommodate their perception of the case to the witness evidence, indicating a stronger tendency to preserve their initial belief. Drawing on previous research on the hindsight bias, Study III tested the hypothesis that the identification of the suspect in a lineup (positive outcome) would increase the perceived suggestiveness of the lineup, whereas a non-identification (negative outcome) would decrease perceived suggestiveness, relative to no outcome knowledge. In a first experiment, undergraduate students (N = 50) showed the predicted influence of positive, but not negative, outcome. In a second experiment, where the lineup was presented as part of a case material, police trainees (N = 126) displayed the expected influence of negative, but not positive, outcome. In Study IV, the appraisal tendencies associated with anger and sadness were expected to (a) shift investigators’ attribution of witness-statement reliability towards either witness variables (anger) or witnessing-situation variables (sadness), and (b) promote either a heuristic (anger) or systematic (sadness) processing of the witness evidence. Experimental data from criminal investigators (N = 61) showed that, when judging statement reliability, sad participants relied on their perception of both witness and situational variables, whereas angry participants relied only on witness variables. Sad participants were sensitive to the consistency of the statement with the central hypothesis of the investigation, indicating systematic processing, whereas angry participants were not, indicating heuristic processing. Taken together, the research in this thesis suggests that investigative judgments are susceptible to motivational, emotional, and cognitive biases. This calls attention to the necessity of developing safeguards against excessive influence of subjective factors in criminal investigations.

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