The insanity defense, also known as the mental disorder defense, is an affirmative defense by excuse in a criminal case, arguing that the defendant is not responsible for their actions due to a psychiatric disease at the time of the criminal act. This is contrasted with an excuse of provocation, in which the defendant is responsible, but the responsibility is lessened due to a temporary mental state. It is also contrasted with the justification of self defense or with the mitigation of imperfect self-defense. The insanity defense is also contrasted with a finding that a defendant cannot stand trial in a criminal case because a mental disease prevents them from effectively assisting counsel, from a civil finding in trusts and estates where a will is nullified because it was made when a mental disorder prevented a testator from recognizing the natural objects of their bounty, and from involuntary civil commitment to a mental institution, when anyone is found to be gravely disabled or to be a danger to themself or to others.
Legal definitions of insanity or mental disorder are varied, and include the M'Naghten Rule, the Durham rule, the 1953 British Royal Commission on Capital Punishment report, the ALI rule (American Legal Institute Model Penal Code rule), and other provisions, often relating to a lack of mens rea ("guilty mind"). In the criminal laws of Australia and Canada, statutory legislation enshrines the M'Naghten Rules, with the terms "defense of mental disorder", "defense of mental illness", or "not criminally responsible by reason of mental disorder" employed. Being incapable of distinguishing right from wrong is one basis for being found to be legally insane as a criminal defense. It originated in the M'Naghten Rule, and has been reinterpreted and modernized through more recent cases, such as People v. Serravo.
In the United Kingdom, Ireland, and the United States, use of the defense is rare. Mitigating factors, including things not eligible for the insanity defense such as intoxication and partial defenses such as diminished capacity and provocation, are used more frequently.
The defense is based on evaluations by forensic mental health professionals with the appropriate test according to the jurisdiction. Their testimony guides the jury, but they are not allowed to testify to the accused's criminal responsibility, as this is a matter for the jury to decide. Similarly, mental health practitioners are restrained from making a judgment on the "ultimate issue"—whether the defendant is insane.
Some jurisdictions require the evaluation to address the defendant's ability to control their behavior at the time of the offense (the volitional limb). A defendant claiming the defense is pleading "not guilty by reason of insanity" (NGRI) or "guilty but insane or mentally ill" in some jurisdictions which, if successful, may result in the defendant being committed to a psychiatric facility for an indeterminate period.
Non compos mentis
Non compos mentis (Latin) is a legal term meaning "not of sound mind". Non compos mentis derives from the Latin non meaning "not", compos meaning "control" or "command", and mentis (genitive singular of mens), meaning "of mind". It is the direct opposite of Compos mentis (of a sound mind).
Although typically used in law, this term can also be used metaphorically or figuratively; e.g. when one is in a confused state, intoxicated, or not of sound mind. The term may be applied when a determination of competency needs to be made by a physician for purposes of obtaining informed consent for treatments and, if necessary, assigning a surrogate to make health care decisions. While the proper sphere for this determination is in a court of law, this is practically, and most frequently, made by physicians in the clinical setting.
In English law, the rule of non compos mentis was most commonly used when the defendant invoked religious or magical explanations for behaviour. An example of religious circumstances which prevent an individual from being guilty due to mental defect can be found in Catholic Canon Law.
History
The concept of defense by insanity has existed since ancient Greece and Rome. During the Roman and Greek eras, insanity was used as a way to help provide a defense for those with mental disorders. 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 their 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. It is likely that the insane, like those under 14, were spared trial by ordeal. When that was replaced by trial by jury, members were expected to find the insane guilty but then to 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. The Criminal Lunatics Act 1800, passed with retrospective effect following the acquittal of James Hadfield, mandated detention at the regent'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 Daniel M'Naghten's acquittal for the homicide of Edward Drummond, whom he mistook for British Prime Minister Robert Peel. The rules define the defense as "at the time of committing the act the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or as not to know that what he was doing was wrong." The key is that the defendant could not appreciate the nature of their 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 their competency to be executed.
In Wainwright v. Greenfield (1986), 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.
In 2006, the US Supreme Court decided Clark v. Arizona, upholding Arizona's restrictions on the insanity defense.
Kahler v. Kansas, 589 U.S. ___ (2020), is a case in which the US Supreme Court justices ruled that the Eighth and the Fourteenth Amendments of the US Constitution do not require states to adopt the insanity defense in criminal cases that are based on the defendant's ability to recognize right from wrong.
Application
The defense of insanity takes different guises in different jurisdictions, and there are differences between legal systems with regard to the availability, definition and burden of proof, as well as the role of judges, juries and medical experts. In jurisdictions where there are jury trials, it is common for the decision about the sanity of an accused to be determined by the jury.
Incompetency and mental illness
An important distinction to be made is the difference between competency and criminal responsibility.
The issue of competency is whether a defendant is able to adequately assist their attorney in preparing a defense, make informed decisions about trial strategy and whether to plead guilty, accept a plea agreement or plead not guilty. This issue is dealt with in UK law as "fitness to plead".
Competency largely deals with the defendant's present condition, while criminal responsibility addresses the condition at the time the crime was committed.
In the United States, a trial in which the insanity defense is invoked typically involves the testimony of psychiatrists or psychologists who will, as expert witnesses, present opinions on the defendant's state of mind at the time of the offense.
Therefore, a person whose mental disorder is not in dispute is determined to be sane if the court decides that despite a "mental illness" the defendant was responsible for the acts committed and will be treated in court as a normal defendant. If the person has a mental illness and it is determined that the mental illness interfered with the person's ability to determine right from wrong (and other associated criteria a jurisdiction may have) and if the person is willing to plead guilty or is proven guilty in a court of law, some jurisdictions have an alternative option known as either a Guilty but Mentally Ill (GBMI) or a Guilty but Insane verdict. The GBMI verdict is available as an alternative to, rather than in lieu of, a "not guilty by reason of insanity" verdict. Michigan (1975) was the first state to create a GBMI verdict, after two prisoners released after being found NGRI committed violent crimes within a year of release, one raping two women and the other killing his wife.
Temporary insanity
The notion of temporary insanity argues that a defendant was insane during the commission of a crime, but they later regained their sanity after the criminal act was carried out. This legal defense developed in the 19th century and became especially associated with the defense of individuals committing crimes of passion. The defense was first successfully used by U.S. Congressman Daniel Sickles of New York in 1859 after he had killed his wife's lover, Philip Barton Key II. The temporary insanity defense was unsuccessfully pleaded by Charles J. Guiteau who assassinated president James A. Garfield in 1881.
Mitigating factors and diminished capacity
The United States Supreme Court (in Penry v. Lynaugh) and the United States Court of Appeals for the Fifth Circuit (in Bigby v. Dretke) have been clear in their decisions that jury instructions in death penalty cases that do not ask about mitigating factors regarding the defendant's mental health violate the defendant's Eighth Amendment rights, saying that the jury is to be instructed to consider mitigating factors when answering unrelated questions. This ruling suggests specific explanations to the jury are necessary to weigh mitigating factors.
Diminished responsibility or diminished capacity can be employed as a mitigating factor or partial defense to crimes. In the United States, diminished capacity is applicable to more circumstances than the insanity defense. The Homicide Act 1957 is the statutory basis for the defense of diminished responsibility in England and Wales, whereas in Scotland it is a product of case law. The number of findings of diminished responsibility has been matched by a fall in unfitness to plead and insanity findings. A plea of diminished capacity is different from a plea of insanity in that "reason of insanity" is a full defense while "diminished capacity" is merely a plea to a lesser crime.
Intoxication
Depending on jurisdiction, circumstances and crime, intoxication may be a defense, a mitigating factor or an aggravating factor. However, most jurisdictions differentiate between voluntary intoxication and involuntary intoxication. In some cases, intoxication (usually involuntary intoxication) may be covered by the insanity defense.
Withdrawal or refusal of defense
Several cases have ruled that persons found not guilty by reason of insanity may not withdraw the defense in a habeas petition to pursue an alternative, although there have been exceptions in other rulings. In Colorado v. Connelly, 700 A.2d 694 (Conn. App. Ct. 1997), the petitioner who had originally been found not guilty by reason of insanity and committed for ten years to the jurisdiction of a Psychiatric Security Review Board, filed a pro se writ of habeas corpus and the court vacated his insanity acquittal. He was granted a new trial and found guilty of the original charges, receiving a prison sentence of 40 years.
In the landmark case of Frendak v. United States in 1979, the court ruled that the insanity defense cannot be imposed upon an unwilling defendant if an intelligent defendant voluntarily wishes to forgo the defense.
Usage
According to an eight-state study, the insanity defense is used in less than 1% of all court cases and, when used, has only a 26% success rate. Of those cases that were successful, 90% of the defendants had been previously diagnosed with mental illness.
A study of racial disparities in the rates of insanity defense found court-appointed mental health professionals are more likely to find that Black criminal defendants are to be determined not criminally responsible as compared to similarly situated white defendants. Another study found sentencing disparities by both race and sex connected to mental disorder diagnoses.
Psychiatric treatment
Those found to have been not guilty by reason of mental disorder or insanity are generally then required to undergo psychiatric treatment in a mental institution, until the person is not a risk to public safety.
In England and Wales, under the Criminal Procedure (Insanity and Unfitness to Plead) Act of 1991 (amended by the Domestic Violence, Crime and Victims Act, 2004 to remove the option of a guardianship order), the court can mandate a hospital order, a restriction order (where release from hospital requires the permission of the Home Secretary), a "supervision and treatment" order, or an absolute discharge. Unlike defendants who are found guilty of a crime, they are not institutionalized for a fixed period, but rather held in the institution until they are determined not to be a threat. Authorities making this decision tend to be cautious, and as a result, defendants can often be institutionalized for longer than they would have been incarcerated in prison.
Worldwide
Australia
In Australia there are nine law units, each of which may have different rules governing mental impairment defenses.
South Australia
In South Australia, the Criminal Law Consolidation Act 1935 (SA) provides that:
269C—Mental competence
A person is mentally incompetent to commit an offence if, at the time of the conduct alleged to give rise to the offence, the person is suffering from a mental impairment and, in consequence of the mental impairment—
(a) does not know the nature and quality of the conduct; or
(b) does not know that the conduct is wrong; or
(c) is unable to control the conduct.
269H — Mental unfitness to stand trial
A person is mentally unfit to stand trial on a charge of an offence if the person's mental processes are so disordered or impaired that the person is —
(a) unable to understand, or to respond rationally to, the charge or the allegations on which the charge is based; or
(b) unable to exercise (or to give rational instructions about the exercise of) procedural rights (such as, for example, the right to challenge jurors); or
(c) unable to understand the nature of the proceedings, or to follow the evidence or the course of the proceedings.
Victoria
In Victoria the current defence of mental impairment was introduced in the Crimes (Mental Impairment and Unfitness to be Tried) Act 1997 which replaced the common law defence of insanity and indefinite detention at the governor's pleasure with the following:
the accused was suffering from a mental impairment; and
the mental impairment affected the accused so they either did not understand the nature and quality of the conduct, or did not know that it was wrong.
These requirements are almost identical to the M'Naghten Rules, substituting "mental impairment" for "disease of the mind".