Also known as:mental disease evidence · evidence of mental disease · mental illness evidence
Written by attorneys · grounded in primary & secondary sources — see below
A category of expert opinion testimony in criminal cases describing a defendant's diagnosed mental disease or defect and its characteristic features. The testimony is typically offered by psychologists or psychiatrists to support an insanity defense or to show that the defendant lacked the mental state required for the charged offense.
Sources & Authorities
How it applies
Common Examples
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Untimely Notice Bars Expert Testimony
Malcolm McKinley pleaded not guilty to arson charges. Six weeks later, after the omnibus deadline, his counsel filed a written notice announcing an intent to rely on a mental disease defense. The prosecutor moved to exclude the psychiatrist's testimony that McKinley suffered from untreated schizophrenia at the time of the fire. The court granted the motion because the notice was filed outside the ten-day window and McKinley failed to show good cause for the delay.
Expert Testimony Limited to Insanity Claim
Melanie Morris was charged with murder after shooting a police officer. She sought to introduce psychiatric testimony that she suffered from paranoid schizophrenia with delusions that government agents were aliens. The trial court permitted the evidence only on the insanity defense and instructed the jury it could not consider the testimony when deciding whether Morris formed the intent to kill. The restriction prevented the jury from using the diagnosis to negate mens rea.
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Model Codes
Casebooks
Clark v. Arizona548 U.S. 735, 752 n.20, 126 S.Ct. 2709, 165 L.Ed.2d 842 (2006)
Common questions
Frequently Asked
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What procedural step must a defendant complete before mental-disease evidence is admissible?+
The defendant must file a written notice of intent to rely on a mental disease or defect defense at the time of the not guilty plea or within ten days thereafter. Late notice is permitted only upon a showing of good cause. Without timely notice the evidence is inadmissible.
Does a change in psychiatric diagnosis after the initial notice invalidate the notice?+
No. The notice requirement is satisfied by a timely written declaration of intent to rely on the defense. The statute does not require a formal diagnosis at the time of filing or a renewed notice when the precise diagnosis later shifts.
May mental-disease evidence be considered on the issue of mens rea in every jurisdiction?+
No. Some jurisdictions restrict mental-disease evidence to the insanity defense and prohibit its use to negate mens rea. The evidence may be admitted only for the limited purpose of showing lack of criminal responsibility.
What showing permits a court to accept an untimely notice of a mental-disease defense?+
The defendant must demonstrate good cause for the delay, such as a recently discovered condition that could not reasonably have been identified earlier. The court then has discretion to permit the late filing.
548 U.S. 735, 126 S. Ct. 2709, 165 L. Ed. 2d 842 (2006)Criminal Law
…or capacity presumption may be placed in issue. First, a State may allow a defendant to introduce (and a factfinder to consider) evidence of mental disease or incapacity for the bearing it can have on the government’s burden to show mens rea . Second, the sanity presumption’s force may be tested in the consideration of an insanity defense…