Impacts of physical and testimonial evidence on South Korean police interrogator’s selection of tactics

Interrogators can hold various types of evidence that affect investigative decision making. In the present study, we examined the effect of evidence type on interrogators’ tactic selection. In a mixed design, we randomly allocated 106 South Korean police interrogators to one of five evidence conditions (between-subject factor). They read a homicide case report in which critical evidence was manipulated with one of the following evidence types: DNA, CCTV, fingerprint, eyewitness, and no evidence. Each scenario entailed the same amount of information, except for critical evidence leading to a suspect’s identity. Officer participants were then asked to choose any tactic from a list of 27 evidential (relating to using evidence; e.g., gradual disclosure of evidence) and non-evidential (not relating to using any type of evidence; e.g., rapport-building skills) interrogation tactics (within-subject factor) to interrogate the suspect in the simulated crime scenario. We measured the number of chosen tactics and calculated the proportion for each type (dependent variable). Results indicated that South Korean interrogators in this experimental setting preferred non-evidential tactics more frequently than evidential ones. Additionally, these non-evidential tactics, such as active listening and identifying basic needs and emotional state, are reported to be commonly employed in their routine interrogations.