An adult with mental retardation who commits a murder should be held legally accountable (assuming the retardation is not so profound as to render him or her incompetent to stand trial). But punishment must be proportionate to both the seriousness of the crime and the defendant's degree of moral culpability.113
Although there are different degrees of mental retardation, in all cases the condition entails serious limitations on the ability to appreciate the consequences and gravity of one's actions and to exercise mature control over one's conduct. An offender with mental retardation should thus never be placed in the category of the most culpable offenders for whom the death penalty is ostensibly reserved.
Categorical exemptions to the death penalty have precedent. In ruling that executing the insane violates the Eighth Amendment's prohibition on cruel and unusual punishment, the U.S. Supreme Court stated:
The U.S. Supreme Court has also ruled that the execution of offenders who committed their crimes before they were sixteen years old violates the Eighth Amendment.115 The court acknowledged that less culpability attaches to a crime committed by a juvenile than to a comparable crime committed by an adult because children lack the experience, perspective, judgment, and intelligence of adults and have less capacity to control their conduct and to think in long-range terms. Given the inherently diminished moral culpability of children, the court held that the imposition of capital punishment for their conduct would be "nothing more than the purposeless and needless imposition of pain and suffering." 116
Human Rights Watch believes that the moral indefensibility of executing a child extends equally to someone who, by virtue of his or her retardation, has cognitive abilities and moral comprehension similar to that of a child. As one state court judge noted in his dissent from a decision permitting the execution of a defendant with mental retardation: "It is incompatible with...a sense of decency and it is morally indefensible...to kill someone who thinks, reasons and operates at the level of a third grader. Executing such a man is comparable to executing an eight-year-old boy."117
113 Tison v. Arizona, 481 U.S. 137 (1987).
114 Ford v. Wainwright, 477 U.S. 390, 410 (1986). Ford addressed the question of whether the Eighth Amendment prohibits the execution of a defendant who has been convicted and sentenced to death but is insane at the time the execution is to occur. U.S. law, drawing on longstanding legal tradition, has held that if a person is determined to be mentally incompetent before trial, he or she cannot be tried at all until competence is regained. Mental illness can also give rise to a finding of "not guilty by reason of insanity."
115 Thompson v. Oklahoma, 487 U.S. 815 (1988). International human rights law, however, forbids the execution of any person who was under the age of eighteen when the crime was committed. International Covenant on Civil and Political Rights, Art.6(5); The Convention on the Rights of the Child, Art.37(a). Of the thirty-eight U.S. states that permit the death penalty, fifteen prohibit executing any person who was under the age of eighteen when the crime was committed. Another four set the minimum age at seventeen. Death Penalty Information Center, "Juveniles," available at www.deathpenaltyinfo.org, visited August 24, 2000.
116 Thompson v. Oklahoma, 487 U.S. at. 838.
117 Lambert v. State, 984 P.2d 221 (Okla. Crim. App. 1999) (Chapel, P.J., dissenting); cert. denied, 528 U.S. 1087 (2000). Judge Chapel dissented from the court's majority opinion approving the execution of a mentally retarded man convicted of murder. The defendant could not make change, spelled no better than a seven-year-old, read at a third-grade level, and had an I.Q. of 68. According to Judge Chapel, the defendant's mental retardation had limited his ability to work or survive.