DSM-5 and Not Guilty by Reason of Insanity and Diminished Mens Rea Defenses

Abstract Courts, defense attorneys, and prosecutors often request assistance from mental health professionals when a criminal defendant’s mental state at the time of the offense is at issue and the defendant enters a mental health defense. This chapter reviews the legal standards addressing the defense of Not Guilty by Reason of Insanity, diminished capacity, and mens rea defenses. Because each of these defenses involves a retrospective analysis of a person’s mental state, evaluators should be familiar with the DSM-5, which represents the most current diagnostic guideline used in the United States. DSM-5 made several changes and additions to how mental disorders are defined, and the potential impact of these changes on the concepts of insanity and other mental health defenses are discussed. General guidelines for conducting an evaluation of a defendant’s criminal responsibility are also provided.