The effect of suspect description and possible motive on forming suspicion during pre-trial investigation: a comparison of police officers and students groups

The initial hypothesis can guide the pre-trial investigator’s decision to form a suspicion regarding the crime. This hypothesis can be based not on all available evidence assessment but intuitive decisions. When initial criminal act assessment is based on expectations or experience, confirmation bias can affect individuals’ decisions. This human cognitive tendency can operate by two mechanisms – selective information search and biased interpretation of information. Confirmation bias can contribute to biased suspicion by leading the investigator to seek and interpret evidence that confirms prior conviction about the crime. Police investigator’s decision to express suspicion towards a specific person can be based on evaluating suspect as criminal and, in that way, affixing the criminal label to suspect. The goal of this study was to find out whether the description of the suspect and possible motive can affect the expression of suspicion and evaluation of available information during criminal act assessment. In a two-part experiment, criminal investigators (N = 40), criminology (N = 63), and law (N = 53) students read a condensed case and had to express suspicion, rate to which extent additional evidence indicated that suspect was involved in the crime and choose further investigation lines. The initial hypothesis was manipulated by providing information about the suspect and motive. Overall, stronger suspicion and biased interpretation of evidence indicative of the suspect’s guilt occurred when a motive and description of the suspect were presented. Professional experience and degree had an impact on the expression of suspicion and biased information interpretation. After reading a criminal case, police investigators expressed stronger suspicion and continued to selectively search for evidence confirming their prior suspicion that the main suspect was involved in the crime, also evaluated all available evidence as indicating the suspect‘s guilt. In this study, students‘ assessments of the crime differed – the expressed suspicion and evaluation of evidence as indicating suspect’s guilt made by law students were significantly weaker than by police investigators