The Making of an Expert Detective. Thinking and Deciding in Criminal Investigations

Abstract: Drawing on theoretical frameworks developed in social and cognitive psychology, this thesis examines the degree to which individual and systemic factors may compensate for inherent biases in criminal detectives’ judgments and decision-making. Study I – an interview study – explored criminal detectives’ views of critical factors related to decision making in homicide investigations. Experienced homicide investigators in Norway (n = 15) and the UK (n = 20) were asked to identify decisional ‘tipping point’– decisions that could change detectives’ mind-set from suspect identification to suspect verification together with situational and individual factors relating to these decisions. In a content analysis, two types of decision were identified as typical and potentially critical tipping-points: (1) decisions to point-out, arrest, or charge a suspect, and (2) decisions concerning main strategies and lines of inquiry in the case. Moreover, 10 individual factors (e.g. experience) and 14 situational factors (e.g. who is the victim) were reported as related to the likelihood of mind-set shifts, most of which correspond well with previous decision-making research. Study II, using a quasi-experimental design, compared the quality of investigative decisions made by experienced detectives and novice police officers in two countries with markedly different models for the development of investigative expertise (England and Norway). In England, accredited homicide detectives vastly outperformed novice police officers in the number of adequate investigative hypotheses and actions reported. In Norway, however, bachelor educated police novices did marginally better than highly experienced homicide detectives. Adopting a similar design and the same stimulus material, Study III asked if a general test of cognitive abilities used in the selection process at the Norwegian Police University College could predict police students’ ability to generate investigative hypotheses. The findings did not support such a notion and this is somewhat in line with the available knowledge in the area showing that cognitive ability tests have low predictability for applied reasoning tasks. Taken together, this thesis suggests that investigative judgments are highly susceptible to the individual characteristics and biases of the detective. The results indicate that detective-expertise might act as a viable safeguard against biased decision-making, but length of experience alone does not predict sound judgments or decisions in critical stages of criminal investigations. Education and training is a solid foundation for the making of an expert detective. Nevertheless all participants’ researched across the two experiments were biased towards crime and guilt assumptive hypotheses. Hence, true abductive reasoning (i.e. to identify all competing explanations) and the presumption of innocence is hard to operationalise even for expert detectives with extensive training.