Limits on Psychiatric Expert Testimony in New York Insanity Cases

Stephan M. Carlson, MD, MBA, FAPA · Criminal Competency and Responsibility

An insanity opinion is bounded on every side. The statute fixes which mental state matters, the rules of evidence fix how far the expert may go, and the jury keeps the one question the expert may not answer. Testimony that ignores those boundaries is not stronger; it is easier to strike. The capacity standard the testimony must track New York's insanity defense is not a verdict on whether a defendant was "mentally ill." It is an affirmative defense, proved by a preponderance, that at the time of the conduct the defendant, as a result of mental disease or defect, lacked substantial capacity to know or appreciate either the nature and consequences of the conduct or that the conduct was wrong (

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