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.
The M'Naghten rule(s) (pronounced, and sometimes spelled, McNaughton) is a legal test defining the defence of insanity, first formulated by House of Lords in 1843. It is the established standard in UK criminal law, and versions have also been adopted in some US states (currently or formerly), and other jurisdictions, either as case law or by statute. Its original wording is a proposed jury instruction:
that every man is to be presumed to be sane, and ... that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing of 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 if he did know it, that he did not know he was doing what was wrong.
In criminal law, diminished responsibility is a potential defense by excuse by which defendants argue that although they broke the law, they should not be held fully criminally liable for doing so, as their mental functions were "diminished" or impaired.
Forensic psychiatry is a subspeciality of psychiatry and is related to criminology. It encompasses the interface between law and psychiatry. According to the American Academy of Psychiatry and the Law, it is defined as "a subspecialty of psychiatry in which scientific and clinical expertise is applied in legal contexts involving civil, criminal, correctional, regulatory, or legislative matters, and in specialized clinical consultations in areas such as risk assessment or employment." A forensic psychiatrist provides services – such as determination of competency to stand trial – to a court of law to facilitate the adjudicative process and provide treatment, such as medications and psychotherapy, to criminals.
In United States federal law, the Daubert standard is a rule of evidence regarding the admissibility of expert witness testimony. A party may raise a Daubert motion, a special motion in limine raised before or during trial, to exclude the presentation of unqualified evidence to the jury. The Daubert trilogy are the three United States Supreme Court cases that articulated the Daubert standard:
A Durham rule, product test, or product defect rule is a rule in a criminal case by which a jury may determine a defendant is not guilty by reason of insanity because a criminal act was the product of a mental disease. Examples in which such rules were articulated in common law include State v. Pike (1869) and Durham v. United States (1954). In Pike, the court wrote, "An accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect."
David Lionel Bazelon was a United States circuit judge of the United States Court of Appeals for the District of Columbia Circuit.
Clark v. Arizona, 548 U.S. 735 (2006), is a United States Supreme Court case in which the Court upheld the constitutionality of the insanity defense used by Arizona.
The Fifth Amendment to the United States Constitution creates several constitutional rights, limiting governmental powers focusing on criminal procedures. It was ratified, along with nine other articles, in 1791 as part of the Bill of Rights.
In criminal law, a mitigating factor, also known as an extenuating circumstance, is any information or evidence presented to the court regarding the defendant or the circumstances of the crime that might result in reduced charges or a lesser sentence. Unlike a legal defense, the presentation of mitigating factors will not result in the acquittal of a defendant. The opposite of a mitigating factor is an aggravating factor.
Bigby v. Dretke 402 F.3d 551, the U.S. Court of Appeals for the Fifth Circuit heard a case appealed from the United States District Court for the Northern District of Texas on the issue of the instructions given to a jury in death penalty sentencing. The decision took into account the recent United States Supreme Court decisions concerning the relevance of mitigating evidence in sentencing, as in Penry v. Lynaugh.
Settled insanity is defined as a permanent or "settled" condition caused by long-term substance abuse and differs from the temporary state of intoxication. In some United States jurisdictions "settled insanity" can be used as a basis for an insanity defense, even though voluntary intoxication cannot, if the "settled insanity" negates one of the required elements of the crime such as malice aforethought. However, U.S. federal and state courts have differed in their interpretations of when the use of "settled insanity" is acceptable as an insanity defense and also over what is included in the concept of "settled insanity".
An ultimate issue in criminal law is a legal issue at stake in the prosecution of a crime for which an expert witness is providing testimony.
Insanity in English law is a defence to criminal charges based on the idea that the defendant was unable to understand what he was doing, or, that he was unable to understand that what he was doing was wrong.
The Insanity Defense Reform Act of 1984 (IDRA) was signed into law by President Ronald Reagan on October 12, 1984, amending the United States federal laws governing defendants with mental diseases or defects to make it significantly more difficult to obtain a verdict of not guilty only by reason of insanity.
United States v. Brawner, 471 F.2d 969, is decision by the United States Court of Appeals for the District of Columbia Circuit in which the Court held that a person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect, he lacked substantial capacity either to appreciate the criminality of his conduct or conform his conduct to the requirements of the law.
The ALI rule, or American Law Institute Model Penal Code rule, is a recommended rule for instructing juries how to find a defendant in a criminal trial is not guilty by reason of insanity. It broadened the M'Naghten rule of whether a defendant was so mentally ill that he is unable to "know" the nature and quality of his criminal act, or know its wrongfulness, to a question of whether he had "substantial capacity to appreciate the criminality of [his] conduct". It also added a volitional component as to whether defendant was lacking in "substantial capacity to conform his conduct to the law". It arose from the case of United States v. Brawner.
Cone v. Bell, 556 U.S. 449 (2009), was a case in which the United States Supreme Court held that a defendant was entitled to a hearing to determine whether prosecutors in his 1982 death penalty trial violated his right to due process by withholding exculpatory evidence. The defendant, Gary Cone, filed a petition for postconviction relief from a 1982 death sentence in which he argued that prosecutors violated his rights to due process under the Fourteenth Amendment by withholding police reports and witness statements that potentially could have shown that his drug addiction affected his behavior. In an opinion written by Justice John Paul Stevens, the Supreme Court held that Cone was entitled to a hearing to determine whether the prosecution's failure to disclose exculpatory evidence violated Cone's right to due process; the Court noted that "the quantity and the quality of the suppressed evidence lends support to Cone’s position at trial that he habitually used excessive amounts of drugs, that his addiction affected his behavior during his crime spree". In 2016, Gary Cone died from natural causes while still sitting on Tennessee's death row.
Kahler v. Kansas, 589 U.S. ___ (2020), is a case of the United States Supreme Court in which the justices ruled that the Eighth and Fourteenth Amendments of the United States Constitution do not require that states adopt the insanity defense in criminal cases that are based on the defendant's ability to recognize right from wrong. It was argued on October 7, 2019 and decided on March 23, 2020.
