States that are most inclined to seek death sentences seem to be incapable of administering the system in a way that reliably and fairly selects the offenders most deserving of the ultimate penalty. Equally dis-heartening, they also seem incapable of exempting offenders who, by virtue of serious mental disability at the time of the crime, are least deserving of execution.
The moral impropriety of executing persons who were not “in their right mind” at the time of the crime was recognized by common-law courts hundreds of years ago. Defendants who were “insane”—who did not know the nature or quality of their acts or that their act was wrong—at the time of the offense were exempt from punishment. However, the test for insanity is typically quite narrow, and judges and juries are skeptical of claims that mental illness should exempt homicide defendants altogether from punishment—and are thus reluctant to find a defendant insane. Only a small fraction of defendants known to be severely mentally ill are acquitted by reason of insanity.
But the moral calculus is considerably different if the issue is whether mentally ill defendants should be executed. This is why contemporary capital sentencing statutes classify “diminished responsibility” due to mental illness at the time of the crime as a mitigating circumstance. In most states, “extreme mental or emotional disturbance” at the time of the offense and “significant impairment of capacity to appreciate the wrongfulness of conduct or to con-form . . . to the requirements of the law” are mitigating circumstances. How-ever, many defense attorneys worry, and research has shown, that evidence of mental illness will amount to a “double-edged sword” such that morally Mental Illness, Diminished Responsibility, and the Death Penalty: A New Frontier By Richard J. Bonnie compelling mitigation narratives of childhood abuse, mental disability, or other frailties of humankind essentially warp from mitigating (i.e., factors in favor of not giving a death sentence) to aggravating (i.e., factors favoring a death sentence). Some attorneys will choose not to present highly relevant evidence of mental illness because of fear that jurors will not consider it, or will view it as evidence of future dangerousness rather than diminished moral culpability. It is precisely to remedy this conundrum that the Supreme Court held in 2002 that individuals with intellectual disability should be categorically exempt from the death penalty. Indeed, the Court worried that because of this “double-edged sword” phenomenon, which applies equally to those with intellectual disability, those who had the lowest moral culpability and were the least deserving of execution were actually more likely to be sentenced to death.
The only way to prevent this pattern of disproportionate capital sentencing, and to ensure that compelling claims of diminished mental responsibility are given adequate moral weight, is to (1) preclude a death sentence if one of these mitigating factors is proved, and (2) require aggressive judicial review of trial court findings that the evidence does not establish diminished responsibility. Unfortunately, that has not happened in most states. The common judicial failure to take seriously the moral importance of proportionality in capital sentencing is one of the rea-sons the Supreme Court has barred the death penalty for juveniles and persons with intellectual disability.
In 2006, the American Bar Association (ABA), American Psychiatric Association, American Psychological Association, and National Alliance on Mental Illness endorsed the principle that a finding of serious mental ill-ness should preclude the death penalty; Mental Health America joined the endorsement in 2011. All of these organizations support the position that:
Defendants should not be executed or sentenced to death if, at the time of the offense, they had a severe mental disorder or disability that significantly impaired their capacity (a) to appreciate the nature, consequences or wrongfulness of their conduct, (b) to exercise rational judgment in relation to conduct, or (c) to conform their conduct to the requirements of the law.
Legislation codifying this principle will be under consideration in several states in 2017, and the ABA has created a Mental Illness Initiative to support this effort. In addition, attorneys for capital defendants and condemned prisoners have used the above consensus statement as the backbone of an argument that imposing the death penalty on these defendants contravenes evolving standards of decency in a civilized society. Several state appellate judges have expressed interest in this argument, and support for such an exemption is likely to grow.
Embracing an exemption for diminished responsibility based on serious mental illness will not rectify the deep injustices of capital sentencing, but it will achieve a modest victory for human dignity.