Federal Rule of Evidence 704 states:
Rule 704. Opinion on ultimate issue
- Except as provided in subdivision (b), testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact.
- No expert witness testifying with respect to the mental state or condition of a defendant in a criminal case may state an opinion or inference as to whether the defendant did or did not have the mental state or condition constituting an element of the crime charged or a defense thereto. Such ultimate issues are matters for the trier of fact alone.
Before Rule 704 was amended in 1984, psychiatrists and other mental health experts were permitted to state opinions as to whether the defendant met the relevant legal test for insanity. This amendment was intended "to eliminate the confusing spectacle of competing expert witnesses testifying to directly contradictory conclusions as to the ultimate legal issue to be found by the trier of fact." See S.Rep. No. 225, 98th Cong., 1st Sess. 230, reprinted in 1984 U.S. Code Cong. & Admin. News 3182, 3412. Thus, it is intended that the expert witnesses' testimony be limited to presenting and explaining their diagnoses, such as whether the defendant had a severe mental disease or defect, and the characteristics of such a disease or defect, if any. Id. While the psychiatrist must be permitted to testify fully, in both clinical and common-sense terms, about the defendant's diagnosis, mental state, and motivation at the time of the alleged act, the determination whether the relevant legal test for insanity has been met is a matter for the legal fact-finder. Id. at 231. See United States v. Edwards, 819 F.2d 262 (11th Cir. 1987). The restriction in Rule 704 on ultimate opinion psychiatric testimony extends to any ultimate mental state of the defendant relevant to ultimate legal conclusions to be proved, such as premeditation in a homicide case, or lack of predisposition in entrapment. Id.
[cited in JM 9-18.000]