Also known as: mental illness · mental defect · insanity defense · mental incapacity
Written by attorneys · grounded in primary & secondary sources — see below
A condition of the mind that impairs a person's ability to understand the nature and consequences of actions or to control conduct in accordance with the law.
Melissa Mills suffered from a progressive mental condition that built over months. When she set fire to a neighbor's shed she later said she felt an overwhelming compulsion she could not resist. The court found that her mental illness prevented her from conforming her conduct to the law and entered an acquittal.
Melanie Morris had been scheduled to testify about a business dispute. Her long-standing mental illness flared into an acute episode that left her unable to attend or testify coherently. The court ruled her unavailable under the mental-illness prong of the unavailability rule.
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Miguel Mendoza had been adjudicated mentally ill and a guardian was appointed over all his property. Without the guardian's involvement he signed a large loan agreement. The court held that the guardianship eliminated his capacity to incur any contractual duties.
Mariam Mansour intended to raise an insanity defense based on a diagnosed mental defect. She filed the required written notice weeks after the pretrial-motion deadline and offered no good-cause explanation. The court refused to allow the defense at trial.
Marco Marquez knew his conduct was legally wrong and that society would condemn it. He nevertheless claimed a mental illness produced an overpowering urge he could not resist. The court ruled that loss of control alone supplied no defense under the traditional M'Naghten test.
Malcolm McKinley entered a complex investment contract while suffering from a mental illness that left him unable to grasp its risks. The other party had reason to know of his condition. The court held the resulting duties were only voidable at Malcolm's option.
Once a court adjudicates mental illness and places the person's property under guardianship, the protected person has no capacity to incur contractual duties. Any contract attempted by that person is treated as lacking effect rather than merely voidable at the protected person's option.
Under the traditional interpretation of M'Naghten the defendant's inability to control behavior or refrain from the crime is irrelevant. A loss of self-control caused by mental illness standing alone does not provide a defense.
A defendant who intends to assert an insanity defense must notify the government in writing within the time provided for filing a pretrial motion. Failure to give timely notice bars reliance on the defense unless the court finds good cause for a late filing.
A declarant is unavailable when the declarant cannot be present or testify because of a then-existing mental illness. The rule treats mental illness as an independent ground of unavailability alongside death and physical illness.
The lack of control need not arise suddenly. It may develop or exist over time as a result of mental illness.
…examiner interviewed appellant while in custody and after the interview issued a Certificate of Medical Examination for Mental Illness. In the certificate, the examiner stated his opinion that appellant was “mentally ill and required hospitalization in a mental hospital.” Art. 5547-42 (Vernon 1958). Appellant retained…