Fed. R. Evid. 704 — Opinion on an Ultimate Issue

(a) IN GENERAL—NOT AUTOMATICALLY OBJECTIONABLE. An opinion is not objectionable just because it embraces an ultimate issue.

(b) EXCEPTION. In a criminal case, an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.