Law & Psychiatry: Does the Constitution Require an Insanity Defense?

Criminal behavior is generally considered to comprise two components: the actus reus, or forbidden act, and the mens rea, or guilty mind. A simple example would be the crime of theft, which requires both taking an item that one does not own (the actus reus) and doing so with the intent of taking someone else’s possession (the mens rea). Were someone to take an object, such as a jacket hanging in a coat room, under the misimpression that the object was his or her own, the act would not constitute a crime because the mens rea of intending to take an item that belongs to someone else would be absent. Except for a small number of “strict liability” crimes, conviction requires proof of both a forbidden act and a culpable intent. If either is lacking, a defendant is not guilty of an offense (6).

The nature of mens rea and its relationship to the defense of insanity have evolved over the centuries. In medieval English law, mens rea was conceived as embodying a moral concept—that is, as requiring intent to injure another person unjustifiably. Thus the 13th century English jurist Bracton (7) wrote, “A crime is not committed unless the will to harm be present.” The early tests for legal insanity (for example, the defendant did “not know what he was doing, no more than an infant, than a brute or wild beast” [8]) were seen as negating mens rea. Defendants who qualified for insanity under such tests would have been so lacking in awareness that even if they had intended to commit the act in question (such as taking an item that they did not own), their mental state would have precluded their acting with the intent to harm another person.

In the 18th and 19th centuries, however, the concept of mens rea began to lose its moral component, being restricted solely to the question of whether the perpetrator intentionally performed the prohibited act (6). Rather than negating mens rea per se, the insanity defense came to be seen as an affirmative defense that could be employed despite the presence of mens rea. Thus a person might recognize that he was taking an object that belonged to another person, but under a test such as the 1843 M’Naghten standard (which asks, in part, whether a defendant knew that he was “doing what was wrong”), he would be entitled to a defense of insanity anyway (9). For example, if the person delusionally believed that he was the messiah and that God therefore had given him the right to take whatever property he desired, he might be found to have mens rea under a narrow conception of the term (that is, he intended to take an object he did not own), but nonetheless he would retain the option to plead insanity under M’Naghten.

In abolishing Idaho’s insanity defense, the state legislature specified that defendants could still introduce evidence of their mental states to negate the mens rea necessary for the crime. But because Idaho follows the narrow version of mens rea that focuses only on intent to perform the prohibited act, some clearly psychotic perpetrators, such as John Delling, would have essentially no mental state defense to the charges against them. Delling knew that he was killing other human beings (although he was motivated by his delusions), which is all that is required under Idaho law for a finding of mens rea.

Unable to assert an insanity defense or a plausible claim that he lacked mens rea, Delling agreed to plead guilty to two counts of second-degree murder, with the understanding that he reserved the right to challenge the state’s rules on insanity. At the sentencing hearing in 2009, the trial judge acknowledged that Delling would meet the standards for an insanity defense, if one existed. But rather than seeing his illness as a mitigating factor, the judge pointed to the meticulous planning that had gone into his delusionally motivated crimes and the uncertainty as to whether his illness would respond to treatment as reasons to fear his ever being in the community again. The court then sentenced him to the maximum penalty on the two counts, life in prison without possibility of parole.

With few options left, Delling exercised his right to appeal to the Idaho supreme court on the grounds that the state’s abolition of the insanity defense violated his constitutional rights to due process (under the 14th Amendment), to present a defense (Sixth Amendment), and to avoid cruel and unusual punishment (Eighth Amendment). As it had in several previous cases, the Idaho court affirmed the validity of the state’s statute (10). Despite the long history of the insanity defense in Anglo-American law, the court held, it did not constitute so fundamental a part of the criminal justice system as to be required by due process. All that was required by the Constitution, according the court, was the opportunity to use mental state evidence to negate the elements of the crime—that is, to disprove mens rea. Of course, Idaho law retained that possibility. The court similarly dismissed the idea that Delling’s Sixth and Eighth Amendment rights had been violated by the abolition of an insanity defense.

In a final effort to overturn his conviction, in 2012 Delling took his case to the U.S. Supreme Court, which had never ruled directly on whether an insanity defense is constitutionally required. In his petition for certiorari (request that the Court hear the case), Delling’s attorneys, two Stanford Law School professors, noted that state supreme courts were in conflict on this question: Nevada’s court had struck down its legislature’s abrogation of the insanity defense, whereas the Idaho, Montana, and Kansas courts had upheld their state’s actions (4). The attorneys quoted previous Supreme Court opinions to the effect that “the Due Process Clause prohibits any imposition of criminal liability that ‘offends [a] principle of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental’” and argued that the insanity defense was such a fundamental principle. In support of this argument, and a similar Eighth Amendment claim, they pointed to the ancient pedigree of the insanity defense and the overwhelming consensus represented by the 46 states and District of Columbia that allowed some version of the plea.

Delling’s position was supported by a variety of groups that submitted friend-of-the-court briefs, including a brief submitted jointly by the American Psychiatric Association and the American Academy of Psychiatry and the Law. The brief noted the ways in which mental illness can affect a person’s ability to appreciate the wrongfulness of his or her behavior and argued that “substantive due process bars serious criminal punishment of a defendant who, because of a mental disorder, lacked a rational appreciation of the wrongfulness of his conduct.” Although states have the discretion to select among a number of insanity standards and to fashion a variety of procedures by which the defense is governed (for example, by putting the burden of proof on the defendant), the brief argued that states must provide some means for defendants to claim that they lacked a rational understanding of the wrongfulness of their actions.

In the end, the Supreme Court declined to hear Delling’s appeal. The justices do not provide explanations for their refusal to entertain particular cases, which requires an affirmative vote of at least four of the nine members of the Court. On rare occasions, however, the justices who would have chosen to hear a case write a dissent from the denial of certiorari, and that happened in Delling (11). Justice Breyer, writing for himself and Justices Sotomayor and Ginsburg, compared two hypothetical cases: “Case One: The defendant, due to insanity, believes that the victim is a wolf. He shoots and kills the victim. Case Two: The defendant, due to insanity, believes that a wolf, a supernatural figure, has ordered him to kill the victim.” He noted that Idaho would accord a mental state defense in the first case, since the defendant, who did not know he was shooting a person, lacked mens rea for murder, but it would not allow such a defense in the second case. Citing the briefs of the APA and other friends of the court, which noted that the circumstances represented by the second case are not uncommon, Justice Breyer implicitly questioned whether Idaho was acting appropriately in drawing a distinction between the cases and indicated that he would have voted to decide that question.

With the majority of the Supreme Court inclined otherwise, however, the message of Delling is that at least for now states are free to abandon the insanity defense if they choose to do so. However, the state that abolished the insanity defense most recently, Kansas, did so nearly two decades ago, and there is no apparent pressure in other states to follow suit. Thus the denial of certiorari in Delling is unlikely to impel other states to preclude defendants from pleading insanity. Moreover, the availability of some sort of insanity defense appears to comport with many people’s instinctive sense that it is unfair to punish a person who, by virtue of mental illness, failed to appreciate the wrongfulness of his or her behavior (12). By permitting this option, although studies indicate it is uncommonly used and infrequently successful (13), our society reaffirms the moral justifications underlying the criminal law.

The author reports no competing interests.