Rule 704. Opinion on Ultimate Issue
(a) 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.
(b) 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 of a defense thereto. Such
ultimate issues are matters for the trier of fact alone.