Also known as: legally insane · insanity defense
Written by attorneys · grounded in primary & secondary sources — see below
A criminal defense that excuses a defendant from liability when a mental disease or defect at the time of the offense caused a lack of substantial capacity either to appreciate the wrongfulness of the conduct or to conform the conduct to the requirements of law.
After receiving Miranda warnings, Lars Lindstrom remained silent during police questioning about an assault. At trial the prosecution sought to introduce that silence to suggest his later insanity claim was fabricated. The court excluded the evidence because post-warning silence cannot be used to rebut an insanity defense.
Lily Lopez was indicted for arson. Her counsel filed written notice of an insanity defense only after discovery closed and after receiving an unfavorable plea offer. The court denied leave to file late because no good cause was shown and therefore barred reliance on the defense at trial.
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The prosecution proved every element of murder beyond a reasonable doubt. Lola Langley then raised legal insanity. The court instructed the jury that the state bore no further burden on the insanity issue and that Langley had to prove the defense by a preponderance of the evidence.
Logan Lane offered expert testimony that a mental disorder prevented him from knowing right from wrong. Arizona applied its abbreviated cognitive-incapacity test. The court upheld the conviction because due process permits a state to select its own formulation of the legal insanity standard.
After a not-guilty-by-reason-of-insanity verdict, Lars Lindstrom was committed to a mental hospital. The state later sought continued confinement under a sexually-violent-predator statute. The court upheld the commitment because the mental abnormality created a likelihood of future dangerous conduct.
Liam Larson was convicted of capital murder after the jury rejected his insanity defense. At the penalty phase he offered psychiatric evidence that a manic episode had impaired his capacity to appreciate wrongfulness. The court admitted the evidence because it was relevant to whether death or life imprisonment was appropriate.
The defendant must show a mental disease or defect that caused a lack of substantial capacity either to appreciate the wrongfulness of the conduct or to conform the conduct to the requirements of law at the time of the offense.
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Written notice must be filed within the time for pretrial motions or at a later time set by the court. Failure to give timely notice bars reliance on the defense unless the court finds good cause for a late filing.
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No. Using post-warning silence to rebut an insanity defense violates the implicit assurance that silence carries no penalty.
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No. Due process permits states to choose among reasonable formulations of the insanity defense. No single canonical test is constitutionally required.
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The state may commit the acquittee if a mental abnormality creates a likelihood of future dangerous conduct, even if the person would otherwise be released after serving a prison term.
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…was ratified. Commonwealth v. York , 50 Mass. 93 (1845).[^maj-8] In 1895 the common-law view was abandoned with respect to the insanity defense in federal prosecutions. Davis v. United States , 160 U. S. 469 (1895). This ruling had wide impact on the practice in the federal courts with respect to the burden of proving various…