Also known as: evidence of mental disease · evidence of mental defect · mental disease evidence
Written by attorneys · grounded in primary & secondary sources — see below
A procedural prerequisite in criminal proceedings that conditions the admissibility of proof offered to show lack of criminal responsibility. The evidence may be introduced only after the defendant files 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, unless the court permits a later filing for good cause.
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Evan entered a not-guilty plea at arraignment on an unauthorized-transfer charge. Eleven days later his lawyer filed written notice that an undiagnosed bipolar disorder rendered him not responsible. The prosecutor moved to exclude all mental-condition testimony. Because the filing fell outside the ten-day window and Evan offered no explanation that could support a good-cause finding, the court granted the motion and barred the evidence.
After a jury rejected Daniel Price's insanity defense and convicted him of capital murder, the defense sought to introduce expert testimony that active psychosis had substantially impaired his capacity to appreciate the wrongfulness of his conduct. The evidence was offered solely to persuade the jury to choose life imprisonment rather than death. The court admitted the testimony because, once guilt has been established, the same category of mental-condition proof becomes relevant to mitigation at the penalty phase.
The evidence remains inadmissible unless the defendant demonstrates good cause and obtains court permission for the late filing. Courts enforce the deadline strictly when no justification for delay is shown.
Supporting sources
No. Once guilt is established, evidence that a mental disease or defect impaired the defendant's capacity to appreciate wrongfulness or conform conduct to law is admissible as mitigation when the jury chooses between death and imprisonment.
…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…
…behavior controls." (Pp. 983-984). 3. The introduction or proffer of past criminal and antisocial actions is not admissible as evidence of mental disease
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No. The statute requires only a timely written statement of intent to rely on the defense. Additional detail about the precise theory is not a precondition of admissibility.
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No. The rule demands a written filing with the court within the prescribed period. Informal communications do not satisfy the requirement or preserve admissibility.
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The notice requirement applies specifically to evidence offered to exclude responsibility under the affirmative defense. Evidence offered solely to negate an element such as intent is governed by ordinary relevance rules and is not subject to the same notice precondition.
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