Insanity defense The insanity defense is a traditional
affirmative defense that dates at least back to
English common law. The codification of the
M'Naghten rules, which have been referenced in one form or another in US law as well as UK law, indicates that someone may be found not guilty of a crime because of a mental condition which prevents them from either controlling their actions or from knowing whether their actions were right or wrong.
Legislative activity In 1995, the state of
Kansas passed a law (Kan. Stat. Ann. § 22-3220) which revoked the traditional
insanity defense. Defendants could no longer argue that, because of their mental illness, they were incapable of deciding right from wrong. Instead, defendants with mental illness were only permitted to argue that their mental illness prevented them from forming the
specific intent (or
mens rea) needed to commit the crime. Supreme Court Justice
Stephen Breyer described the distinction between the two systems in his dissent in
Delling v. Idaho, a case covering the same topic that the Supreme Court declined to hear in 2012: Case One: The defendant, due to insanity, believes that the victim is a wolf. He shoots and kills the victim. Case Two: The defendant, due to insanity, believes that a wolf, a supernatural figure, has ordered him to kill the victim. In Case One, the defendant does not know he has killed a human being, and his insanity negates a mental element necessary to commit the crime. In Case Two, the defendant has intentionally killed a victim whom he knows is a human being; he possesses the necessary mens rea. In both cases the defendant is unable, due to insanity, to appreciate the true quality of his act, and therefore unable to perceive that it is wrong. But … the defendant in Case One could defend the charge by arguing that he lacked the mens rea, whereas the defendant in Case Two would not be able to raise a defense based on his mental illness. As of 2020, at least four other states have passed laws which are conceptually similar to Kansas's:
Idaho,
Alaska,
Utah, and
Montana Kahler murder case In late 2009, James Kahler was arrested and charged with four counts of
first-degree murder with the murder of four members of his family: his wife, his wife's grandmother, and his two teenage daughters. During his trial, his defense argued that he had mentally 'snapped' following his divorce and job loss. At the time of the murder, they asserted that he suffered from depression Despite this testimony, he was found guilty of each murder and
sentenced to death at the end of August 2011.{{cite web| url=https://www.columbiamissourian.com/news/update-jury-sentences-kahler-to-death-in-quadruple-slaying/article_727ae23f-7d7d-5297-b4fa-cb3cdd554e38.html == In lower courts ==