Mo. Rev. Stat. § 562.086: Lack of responsibility because of mental disease or defect.

1. A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he was incapable of knowing and appreciating the nature, quality or wrongfulness of his or her conduct.

2. The procedures for the defense of lack of responsibility because of mental disease or defect are governed by the provisions of chapter 552.