The insanity defense has been of special interest to psycholegal scholars. Despite its notoriety, the defense is infrequently used and rarely successful. Yet, it is surrounded by myths and misconceptions. These misconceptions put the credibility of our legal system at stake since it can cause biased jurors to judge criminal acts based on their own misconstruals of what it means to find a defendant Not Guilty By Reason of Insanity (NGRI). In order to understand and eventually counteract these biases, it is important to first understand what they are. In recent years, developments in aggression research have strengthened the link between psychology and criminal law. Most notably, the reactive/instrumental dichotomy of aggression has been suggested as a model by which both fields can understand and explain behavior. The dichotomy has had many legal applications but has yet to be used to examine the insanity defense. The purpose of the current study was to examine how attributions of reactive and instrumental aggression as well as the defendant's level of psychosis and injury to victim affect the outcome of NGRI cases. This study further explored whether police officers would make distinct attributions of reactive and instrumental aggression, or assume one general dimension of aggression. Participants were 101 defendants in the state of Wisconsin who had pleaded NGRI. The data were collected during the defendant's competency to stand trial hearings and were based on police reports of the defendant's violent offenses.In the first model, reactive and instrumental aggression were treated as separate factors. In the second model, they were combined into one factor of premeditation. Structural Equation Modeling of the data did not reveal good fit, but indicated a few significant pathways. Given these results, further exploratory and confirmatory analyses were run. Results indicated that police officers rated aggressive behavior as one factor (premeditation) and that premeditation was the only significant predictor of outcome. These findings suggest that jurors, and potentially judges, may have certain biases toward defendants whose cases indicate a high level of planning. Possible implications and future directions are discussed.

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