The effects of motive information and crime unusualness on jurors' judgments in insanity cases.

This study investigated the effects of motive information and crime unusualness on mock jurors' judgments in two homicide cases in which the defendant pleaded insanity. Undergraduates (N = 371) read case information and rendered a verdict, estimated the probability that the defendant was insane, and made additional judgments about the defendant's mental state. The defendant was more likely to be judged insane if the crime was oddly committed rather than committed in a typical manner. Prosecution motive information also affected judgments; the defendant was considered more sane if the prosecution presented evidence of a strong, reasonable motive. Evidence of a "crazy," unreasonable motive, presented by the defense, caused jurors to see the defendant in one of the cases as more insane.