Expert Opinion and the Insanity Defense

The insanity defense has come a long way since 1843, the year Daniel M’Naghton shot British Prime Minister Robert Peel’s secretary Edward Drummond by mistake. Under the M’Naghton Rule, an accused could escape conviction if a mental disability either prevented the accused from knowing the nature and quality of an act or prevented the accused from knowing the difference between right and wrong.

That was the law of Tennessee until 1977. Then Justice Henry filed Graham v. State, 547 S.W.2d 531, adopting the Model Penal Code test.

In 1995 the General Assembly enacted the present law, codified at Tenn. Code Ann. §39-11-501:

(a) It is an affirmative defense to prosecution that, at the time of commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature or wrongfulness of the defendant’s acts. Mental disease or defect does not otherwise constitute a defense. The defendant has the burden of proving the defense of insanity by clear and convincing evidence.

(b) As used in this section, mental disease or defect does not include any abnormality manifested only by repeated criminal or otherwise antisocial conduct.

(c) No expert witness may testify as to whether the defendant was or was not insane as set forth in subsection (a). Such ultimate issue is a matter for the trier of fact alone.

Obviously the insanity defense is not an easy option. The accused is saddled with an affirmative defense. And the burden of proof is the heavy “clear and convincing” version.

Let’s turn now to expert opinion. The quoted statute at subsection (c) precludes opinions on the ultimate issues of sanity or insanity. Tenn. R. Evid. 704, however, seems contra: “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.” But the 1996 Advisory Commission Comment refers to the insanity prohibition in the Code. And note that Fed. R. Evid. 704 expressly states the prohibition, added by Congress in 1984 after John Hinckley was adjudicated insane in his trial for the attempted assassination of President Reagan.

Although a psychiatrist or psychologist cannot tell a jury that “He’s sane” or “She’s insane,” these professionals can dance around the ultimate issue. They can describe in detail the mental problems of patients. Just caution your experts not to cross the line.

Check Tenn. R. Crim. P. 12.2 for two crucial procedural requirements. If you intend to assert the insanity defense you must give the prosecutor written notice. Likewise, if you intend to introduce expert testimony on your client’s mental condition you must notify the prosecutor in writing.

Finally, let me recommend Judge Mark Ward’s treatise on Tennessee Criminal Trial Practice (West 2012). At §23:10 he covers the insanity defense.


Don Paine DONALD F. PAINE is a past president of the Tennessee Bar Association and is of counsel to the Knoxville firm of Paine, Tarwater, and Bickers LLP. He lectures for the Tennessee Law Institute.