Also known as: insanity defence · insanity defenses · insanity defences · NGRI · not guilty by reason of insanity
Written by attorneys · grounded in primary & secondary sources — see below
An affirmative defense in criminal law alleging that a mental disease or defect caused the accused to commit the charged offense. A successful assertion produces a special verdict of not guilty by reason of insanity that typically results in involuntary commitment to a mental institution rather than outright acquittal.
Ivan Ivanov was arrested for assault and received Miranda warnings. He remained silent during questioning. At trial Ivan asserted an insanity defense based on schizophrenia. The prosecutor attempted to introduce Ivan's post-warning silence to suggest the defense was fabricated. The court excluded the evidence because the prosecution may not use post-Miranda silence to rebut an insanity defense.
Ike Ingram was charged with arson. His counsel intended to raise an insanity defense but filed the required written notice two weeks after the pretrial-motion deadline. The government moved to bar the defense. The court granted the motion and precluded Ike from relying on insanity because he failed to provide timely notice under the rule.
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Ivy Ibarra set fire to her apartment building while experiencing acute paranoid delusions that neighbors were poisoning her water supply. Expert testimony established that the delusions stemmed from untreated schizophrenia. The court instructed the jury that Ivy would be acquitted if the arson was the product of her mental disease. The jury returned a not-guilty-by-reason-of-insanity verdict.
India Inoue was charged with murder. She raised an insanity defense and presented psychiatric evidence of bipolar disorder. The trial court instructed the jury that India bore the burden of proving insanity by a preponderance of the evidence. The jury rejected the defense and convicted her.
Isabella Ingram, an indigent defendant charged with homicide, notified the court she would assert an insanity defense. She requested appointment of a psychiatrist to evaluate her mental state at the time of the offense. The trial court denied the request. The appellate court reversed, holding that the state must provide psychiatric assistance when an insanity defense is likely to be raised.
Ingrid Innes was charged with robbery. A psychiatric report suggested she may have been insane at the time of the offense. Ingrid nevertheless entered a guilty plea to avoid indefinite commitment. The court accepted the plea after confirming it was voluntary and intelligent.
A successful insanity defense produces a special verdict of not guilty by reason of insanity. The defendant is typically committed to a mental institution rather than released.
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Yes. Under federal rules a defendant must file written notice of intent to assert an insanity defense 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 absent good cause.
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No. The prosecution may not introduce evidence of post-Miranda silence to rebut or counter an insanity defense because such use violates the implicit assurance that silence carries no penalty.
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Yes. When a defendant makes a preliminary showing that an insanity defense is likely, the state must provide access to a psychiatrist to assist in preparing and presenting the defense.
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The defendant bears the burden of proving insanity. States may constitutionally place that burden on the defendant by a preponderance of the evidence.
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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…