Current Application of the Insanity Defense
The question of who has the burden of proof with an insanity defense has been a source of controversy. Before the Hinckley verdict, a majority of states had the burden of proof rest with the state; that is, the prosecutor had to prove that the defendant was not insane. After the Hinckley verdict, the vast majority of states required the defense to prove that the defendant was indeed insane. In states where the burden is on the defense to prove insanity, the defense is required to show either by clear and convincing evidence or by a preponderance of the evidence that the defendant is insane. In states where the burden is still on prosecutors to prove sanity, they are required to prove it beyond a reasonable doubt.
Contrary to uninformed opinion, defendants found not guilty by reason of insanity are not simply released from custody. They are generally committed to mental hospitals where they can be confined for longer than their prison terms would have been. In the case of Jones v. United States, the Supreme Court in 1983 backed this proposition, ruling that the sentence that criminal defendants would have received had they been convicted should have no bearing on how long they could be committed to a mental hospital.
After Hinckley, many states changed their commitment policies to ensure that a defendant found not guilty by reason of insanity would be required to stay in a mental hospital for a certain period of time for evaluation following acquittal. Previously, no time was specified. Also, several states changed the burden of proof for release from the state to defendants.
All jurisdictions require that criminal defendants must be competent to stand trial, meaning that defendants understand the nature of the proceedings against them and are able to assist counsel in their defense. A person who is found to be mentally incompetent to stand trial is usually hospitalized for treatment until such time that the person is competent to stand trial. Competency does not address the guilt or innocence of a party, and so competency to stand trial should not be confused with the insanity defense.
The federal Insanity Defense Reform Act of 1984, codified at 18 U.S.C. § 17, provides: "It is an affirmative defense to a prosecution under any Federal statute that, at the time of the 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 and quality of the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense." This act, a response to the Hinckley verdict, eliminated the Irresistible Impulse Test from the insanity defense under federal law. The act also provided that "the defendant has the burden of proving the defense of insanity by clear and convincing evidence." Previously under federal law, the government had the burden of proving sanity.
Finally, the Hinckley verdict accelerated the adoption of "guilty but mentally ill" verdicts by states. The "guilty but mentally ill" verdict allows mentally ill defendants to be found criminally liable and requires them to receive psychiatric treatment while incarcerated, or, alternatively, to be placed in a mental hospital and then, when they are well enough, to be moved to a prison to serve their sentences. Laws allowing pleas and verdicts of guilty but mentally ill were first adopted in Michigan in 1975, and concurrent with or subsequent to the Hinckley trial were adopted by 12 more states.