Also known as: mental disease · mental defect · mental diseases or defects · insanity defense · mental incapacity
Written by attorneys · grounded in primary & secondary sources — see below
An abnormal mental condition that substantially impairs cognitive or volitional capacities. The condition excuses criminal responsibility when it produces the charged conduct or negates a required mental state.
Miranda Morales, diagnosed with severe schizophrenia, set fire to a vacant building after delusions convinced her the structure housed government surveillance equipment. She would not have committed the arson but for the delusions. The court acquitted her under the Durham rule because the offense was the product of her mental disease or defect.
Malcolm McKinley faced a capital murder trial. Expert testimony showed his longstanding bipolar disorder substantially impaired his ability to appreciate the wrongfulness of the killing. The jury considered the evidence of mental disease or defect and recommended life imprisonment rather than death.
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Matthew Martinez intended to raise an insanity defense based on a documented psychotic episode. He filed the required written notice only after discovery closed and after receiving an unfavorable plea offer. The court refused to allow the late filing for lack of good cause, barring reliance on the defense.
Marco Marquez was acquitted of assault by reason of mental disease or defect. The court immediately ordered him committed to the custody of the Commissioner of Mental Hygiene for placement in an appropriate institution for custody, care, and treatment.
Maria Morales was charged with murder. She introduced evidence of long-term psychosis that prevented her from forming the required intent. The court instructed the jury that the government bore the burden of proving her sanity beyond a reasonable doubt.
Ming Ma was convicted of capital murder. Evidence established that he had an IQ of 65 and significant adaptive deficits caused by a congenital mental defect. The court vacated the death sentence because executing a person with such a mental defect violates the Eighth Amendment.
The defendant must show that the charged offense was the product of a mental disease or defect. This requires proof that the defendant would not have committed the crime but for the condition.
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Evidence that the defendant's capacity to appreciate the criminality of the conduct or to conform conduct to the law was impaired by mental disease or defect is admissible in favor of a sentence of imprisonment.
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The defendant cannot rely on the insanity defense. The court may permit a late filing only upon a showing of good cause.
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The court must order the defendant committed to the custody of the appropriate mental health authority for placement in an institution for custody, care, and treatment.
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The prosecution must prove beyond a reasonable doubt that the defendant was sane at the time of the offense.
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Yes. Execution of a person with intellectual disability caused by a mental defect violates the Eighth Amendment.
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