Also known as: insanity defense · insanity defences · insanity defence · insanity plea
Written by attorneys · grounded in primary & secondary sources — see below
An affirmative defense in criminal proceedings that excuses liability when a mental disease or defect at the time of the offense caused the defendant to lack substantial capacity to appreciate the wrongfulness of the conduct or to conform the conduct to the requirements of law. The defense requires the defendant to give timely written notice to the government. The prosecution may not use post-Miranda silence to rebut the defense.
Select any source to read its text and confirm it supports the definition.
Danielle Dixon was arrested for assault and received Miranda warnings. She remained silent during questioning. At trial she raised an insanity defense based on schizophrenia. The prosecution sought to introduce her post-warning silence to show she understood her actions were wrongful. The court excluded the evidence.
Damian Decker planned to assert insanity after a violent episode tied to delusions. He filed written notice only after discovery closed and after receiving an unfavorable plea offer. The government moved to preclude the defense. The court denied leave to file late because no good cause was shown.
Destiny Davis made a preliminary showing that her bipolar disorder would be central to an insanity claim at trial. The state refused to fund a defense psychiatrist. The court ordered the state to provide access so Davis could prepare and present the defense effectively.
Daphne Doyle cut fences and released livestock onto a highway while fixated on delusions that the animals were government drones. Medical evidence showed her PTSD and dissociative episodes produced the conduct. The court applied the product test and acquitted her because the offense resulted from the mental disease.
Dominic Drake raised insanity after a charged assault. The jurisdiction placed the burden of proving the defense on the defendant. Drake presented expert testimony on his schizophrenia. The jury found he failed to meet the burden and convicted him.
Daniel Diaz asserted insanity in a murder prosecution. The state proved every element of the offense beyond a reasonable doubt. Diaz bore the burden only on the insanity defense. The jury rejected the defense and returned a guilty verdict.
The defendant must prove a disease of the mind caused a defect in reasoning that left the defendant unable to understand the nature and quality of the act or to know that the act was wrongful under societal standards. Personal moral belief that the conduct was justified is insufficient if the defendant retained capacity to recognize that society regards the conduct as wrong.
Supporting sources
…issue in Leland v. Oregon was the constitutionality under the Due Process Clause of the Oregon rule that the defense of insanity must be proved by the defendant beyond a reasonable doubt. Nothing that Davis "obviously establish[ed] no constitutional doctrine," 343 U. S., at 797, the Court refused to strike down the…
…the State could quite consistently with such a constitutional principle conclude that a defendant who sought to establish the defense of insanity, and thereby escape any punishment whatever for a heinous crime, should bear the laboring oar on such an issue. Footnotes — Concurring opinion · [^conA- ] [^conA-1]: While Fay v.…
…in question, and suggested that this mental illness might have begun many years earlier. App. 35. Finally, Oklahoma recognizes a defense of insanity
…43 U. Cin. L. Rev. 781 (1974). Indeed, the notion of an "irresistible impulse" often has helped to shape criminal law's insanity defense
…reverse the conviction (1) because the trial court did not correctly apply existing rules governing the burden of proof on the defense of insanity
A defendant must notify the government in writing within the time for filing pretrial motions or at a later time set by the court and must file a copy with the clerk. Failure to provide timely notice bars reliance on the defense unless the court finds good cause for a late filing.
Supporting sources
No. The prosecution may not introduce post-Miranda silence as evidence to rebut or counter an insanity defense because such use violates the implicit assurance that silence carries no penalty.
Supporting sources
A state may constitutionally require the defendant to prove the affirmative defense of insanity by a preponderance of the evidence provided the prosecution retains the burden of proving every element of the offense beyond a reasonable doubt.
Supporting sources
When the defendant makes a preliminary showing that sanity at the time of the offense is likely to be a significant factor at trial, the state must provide access to a psychiatrist to assist in preparing and presenting the defense.
Supporting sources