Insanity defense  

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In criminal trials, the insanity defense is where the defendant claims that because of psychiatric illness they were not responsible for their actions. The exemption of the insane from full criminal punishment dates back to at least the Code of Hammurabi. There are different views of the insanity defense, each of which have their merits. Some view it as a status defense; some see it as relating to lack of mens rea; others see it as an excuse. There are different definitions of legal insanity, which is a legal term of art not a medical term. There are the M'Naghten Rules, the Durham Rule, the Americal Legal Institute definition, and various miscellaneous provisions e.g. relating to lack of mens rea. The chief distinction of the M'Naghten Rules is that there is no volitional limb - that is to say that irresistible impulse does not conform to the M'Naghten Rules definition of insanity.

In the United Kingdom, Ireland and the United States, use of the defense is rare; it is more common to rely upon a state of temporary mental impairment. In the United States, this is not a legal defense, but a mitigating factor referred to as "diminished capacity". Mitigating factors, including things not eligible for the insanity defense like intoxication, may lead to reduced charges or reduced sentences. The insanity defense is available in most jurisdictions that respect human rights and have a rule of law although the extent to which it can be applied differs between jurisdictions.

The insanity defense is based on evaluations by forensic professionals that the defendant was incapable of distinguishing between (legal) right and wrong or appreciating the nature of his or her actions at the time of the offense. Some jurisdictions require the evaluation to address the defendant's ability to control his or her behavior at the time of the offense (the volitional limb). A defendant making the insanity argument might be said to be pleading "not guilty by reason of insanity" (NGRI) which, if successful, may result in the defendant being committed to a psychiatric facility for an indeterminate period.

Diminished responsibility or diminished capacity can be employed as a mitigating factor and in the United States is applicable to more circumstances than the insanity defense. For example, some jurisdictions accept inebriation or other drug intoxication as mitigating factors whilst intoxication is not accepted as an insanity defense on its own. If diminished responsibility or capacity is presented convincingly, the charges may be reduced to a lesser offense or the sentence may be more lenient.

History of the insanity defense

The concept of defense by insanity has existed since ancient Greece and Rome. However, in colonial America a delusional Dorothy Talbye was hanged in 1638 for murdering her daughter, as at the time Massachusetts's common law made no distinction between insanity (or mental illness) and criminal behavior. Edward II, under English Common law, declared that a person was insane if his or her mental capacity was no more than that of a "wild beast" (in the sense of a dumb animal, rather than being frenzied). The first complete transcript of an insanity trial dates to 1724 (Rex v. Arnold). It is likely that the insane, like those under 14, were spared ordeal by trial. When trial by jury replaced this, the jury members were expected to find the insane guilty but then refer the case to the King for a Royal Pardon. From 1500 onwards, juries could acquit the insane, and detention required a separate civil procedure (Walker, 1985) . The Criminal Lunatics Act 1800, passed with retrospective effect following the acquittal of James Hadfield, mandated detention at his or her majesty's pleasure (indefinitely) even for those who, although insane at the time of the offence, were now sane.

The M'Naghten Rules of 1843 were not a codification or definition of insanity but rather the responses of a panel of judges to hypothetical questions posed by Parliament in the wake of M'Naghten's acquittal for the homicide of Edward Drummond, who he mistook for British Prime Minister Robert Peel. The rules define the defense as "at the time of the commission of the acts constituting the offense, the defendant as a result of a severe mental disease or defect, was unable to appreciate the nature and quality of the wrongfulness of his acts." The key is that the defendant could not appreciate the nature of his actions during the commission of the crime.

In Ford v. Wainwright 477 U.S. 399 (1986), the US Supreme Court upheld the common law rule that the insane cannot be executed. It further stated that a person under the death penalty is entitled to a competency evaluation and to an evidentiary hearing in court on the question of his competency to be executed.

In Wainwright v. Greenfield, the Court ruled that it was fundamentally unfair for the prosecutor to comment during the court proceedings on the petitioner's silence invoked as a result of a Miranda warning. The prosecutor had argued that the respondent's silence after receiving Miranda warnings was evidence of his sanity.

See also

• Settled insanity
• Diminished responsibility
• Henry de Bracton
• Mental disorder defence
• Intoxication defence
• Sanity
• Twinkie defense
• Satis furore ipso punitur and fati infelicitas excusat, concepts from Roman law
• Crime and insanity in England (1968) Nigel Walker
• the trial of Laurence Shirley, 4th Earl Ferrers.
• M'Naghten rules