Rule 704(b) of the Federal Rules of Evidence provides:
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.
The question is: Does Rule 704(b) permit a government expert witness to
testify about certain roles in criminal activity, that people in those roles are
knowing participants in the criminal activity, and then that a particular
defendant played one of those roles in the case at bar?

Does Rule 704(b) permit a government expert witness to testify about certain roles in criminal activity, that people in those roles are knowing participants in the criminal activity, and then that a particular defendant played one of those roles in the case at bar?