Preliminary investigations of crimes often take place under pressure from various types of demands, such as shortage of time, norms in the work culture of the police, and expectations from the media and the general public.

These demands can create a conflict between the goals, on the one hand, to carry out as correct and objective an assessment of the case as possible and, on the other hand, to reach quick results and ‘solutions.’

Two of the studies in Ask’s dissertation focus on police officers’ evaluation of evidence under such conditions. It was found, for one thing, that the need to reach a quick result increased the risk of investigators not being able to move away from their original hypothesis in a case and not being able to take into consideration evidence that is uncovered later in the investigation.

This motivation also seems to lead to an inability to find information that works against their own hypothesis.

Moreover, crime investigators often encounter events that arouse strongly negative feelings, such as a brutal beating or a family tragedy.

The dissertation studied how such emotional reactions affect police officers’ interpretation of evidence in the investigation of a violent crime, and it was found that depressed and angry police officers had radically different interpretations of cases.

Angry evaluators evinced great similarities with those who had wanted quick results in earlier studies, since they were unable to free themselves of their first impressions of the case. Depressed evaluators, on the other hand, were receptive to information that turned up in a later stage of the investigation.

The reliability of testimony was also assessed differently by police officers in different affective states. Depressed evaluators, compared to angry ones, were more willing to factor in the situation in which the witness had observed the crime.

Throughout the studies it was found that one and the same piece of evidence was looked upon in different ways depending on whether it supported or undermined the hypothesis of the investigator in the case.

Objective facts, such as the conditions under which the crime was witnessed, were evaluated more critically if the testimony conflicted with the investigators’ expectations than if they confirmed them. This indicates that there is considerable scope for interpretation when it comes to information central to crime investigations.

It has long been known that people’s judgments and decisions are influenced by emotional states, desires, and needs.

The dissertation concludes that judgments made by police officers are no exception to these universal phenomena. The findings therefore point to a need to raise the awareness of these risk factors and to develop security measures to minimize their influence, thereby safeguarding our civil rights as citizens under the rule of law.

Title of dissertation: Criminal investigation: motivation, emotion and cognition in the processing of evidence

Author of dissertation: Karl Ask, phone: +46 31-841889 (home), +46 31-773 1937 (office)

e-mail: karl.ask@psy.gu.se