Insanity defense Summary

  • Last updated on November 11, 2022

Not guilty plea entered by a criminal defendant on the grounds that an impaired mental condition makes him or her unable to understand the wrongfulness of the act committed.

For most of U.S. history, insanity determinations were the province of the states, with intrastate consistency maintained by appellate court decisions and state statutes. Inconsistencies appeared among the states on a number of issues: the breadth of the insanity definition employed, permissible evidence and testimony, and the posttrial disposition of an insane defendant. Most states relied on the M’Naghten ruleM’Naghten rule[MNaghten rule] (created in 1843 in England by the House of Lords), which restricts insanity to a mental condition sufficiently debilitating to preclude “knowing the nature and consequences of the criminal act.” The most common posttrial disposition of a legally insane defendant was an indefinite and long period of institutionalization.

In the mid-twentieth century, two contrasting cultural trends encouraged the Supreme Court to examine the procedures and consequences of the insanity defense. These trends were an emerging concern with the civil liberties of the mentally impaired criminal defendant and a growing fear of crime that highlighted the need of the state to protect the public from criminally insane individuals.

A series of Court decisions protected the due processDue process, procedural rights of a mentally ill defendant to plead not guilty by reason of insanity. The court ruled in Ake v. Oklahoma[case]Ake v. Oklahoma[Ake v. Oklahoma] (1985) that a psychiatric expert must be provided for an indigent defendant who wished to plead insanity. In Riggins v. Nevada[case]Riggins v. Nevada[Riggins v. Nevada] (1992), the Court ruled that defendants who plead not guilty by reason of insanity may refuse, at the time of their testimony, to take medication that will reduce or eliminate symptoms. It also found, in Jones v. United States[case]Jones v. United States[Jones v. United States] (1983) and Foucha v. Louisiana[case]Foucha v. Louisiana[Foucha v. Louisiana] (1992), that the release of someone found not guilty by reason of insanity depends on that individual’s recovery from the mental condition, not the expiration date of the sentence for the alleged offense.

At the same time, the Court recognized the police powersPolice powers of the state to protect the public from dangerous deranged people. In Leland v. Oregon[case]Leland v. Oregon[Leland v. Oregon] (1952), the Court upheld state laws that made an insanity plea more difficult by placing the burden of proof on the defendant. In Hendricks v. Oklahoma[case]Hendricks v. Oklahoma[Hendricks v. Oklahoma] (1997), the Court refused to extend due process safeguards to such categories of offenders as sexual predators, who may be institutionalized indefinitely beyond their prescribed sentence.

Public concern with insanity as a loophole grew most intense after 1983 when John Hinckley, attempted presidential assassin, was found not guilty by reason of insanity and hospitalized. Several states tried to reduce the use of insanity pleas by adding an alternative guilty but mentally ill category of offender, who was treated, then punished. Other state courts, in contrast, continued to employ definitions of insanity broader than that set forth in the M’Naghten rule, encompassing “irresistible impulses” by lucid people. Challenges to such definitional variations are consistently dismissed by the Court. Although the scope of insanity definitions varies widely, the underlying relevance of criminal intent remains broadly accepted and constitutionally solid.

Further Reading
  • Steadman, Henry J., et al. Before and After Hinckley: Evaluating Insanity Defense Reform. New York: Guilford Press, 1993.
  • Wrightsman, Lawrence, Michael Nietzel, and William Fortune. Psychology and the Legal System. Brooks/Cole, 1998.

Common law

Due process, procedural

Indigent criminal defendants

Police powers

Sixth Amendment

Categories: History Content