In 1972, a large splinter of wood ricocheted off Cecil Clayton’s saw blade and pierced his skull in his left temple. The injury destroyed 20 percent of Clayton’s frontal lobe—about eight percent of his brain overall—and changed his life. One of his brothers later testified that after the accident, Clayton “broke up with his wife, began drinking alcohol and became impatient, unable to work and more prone to violent outbursts.” His reading and writing skills dropped to third- and fourth-grade levels, respectively, and he started to suffer from hallucinations, paranoia, and other psychiatric symptoms.

In 1996, roughly 24 years after his original accident, Clayton shot and killed police officer Christopher Casetter, who had been called to a domestic dispute. A Missouri jury found Clayton guilty and sentenced him to death. On Saturday, a sharply divided Missouri Supreme Court ruled 4-3 against his procedural request for a mental competency hearing before his execution. Unless the U.S. Supreme Court or Governor Jay Nixon intervenes, the state of Missouri will execute the 74-year-old Clayton on Tuesday afternoon.

The Missouri Supreme Court ruling raises serious questions about the constitutionality of Clayton’s execution. The Supreme Court has repeatedly ruled that the Eighth Amendment forbids the execution of persons whose mental illness or intellectual disability prevent them from understanding the consequences of their actions or why they are being put to death. The Court’s rationale for this prohibition was that ending a person’s life for reasons they cannot understand serves “no legitimate penological purpose,” and is therefore cruel and unusual.

After Missouri set his March 17 execution date in January, Clayton’s attorneys petitioned the courts for a competency hearing, hoping to establish his intellectual disability and prevent his execution. The Supreme Court has ruled that inmates have a due-process right to a mental competency hearing once their execution date is set. At these hearings, inmates can present evidence and testimony to demonstrate their incapacity for execution to a neutral fact-finder.

The decision by the Missouri Supreme Court denied Clayton the chance to have such a hearing. Four of the seven judges ruled that Clayton did not meet the “substantial threshold showing,” established to prevent frivolous claims from unnecessarily slowing down the system. If inmates do not meet this cursory level, they can’t seek a full review and its potential for relief. Clayton’s lawyers argued that the obvious brain injury and testimony from three psychiatrists who examined him easily meet this cursory procedural hurdle.

The Missouri Supreme Court disagreed. The majority’s ruling extensively reviewed Clayton’s legal and medical history, disputed expert psychologists’ credibility, attacked their conclusions about his mental capabilities, and weighed Clayton’s past competency arguments during his trial and sentencing phase. In their petition to the U.S. Supreme Court on Monday, Clayton’s lawyers argued “the Missouri Supreme Court…essentially required Clayton to prove his incompetency in order to obtain a hearing on his incompetency.”

Three dissenters, led by Judge Laura Stith, accused the majority of “putting the cart before the horse” by denying the competency hearing. She criticized the use of Clayton’s trial competency, reminding her colleagues that “the issue here is not whether Mr. Clayton was sufficiently competent to assist in his defense or to be found guilty when he was convicted in 1996 [but] whether Mr. Clayton is sufficiently competent today to be executed.” Stith noted that neither a jury nor a Missouri court had considered Clayton’s most recent IQ score of 71, nor had they evaluated the psychiatrists’ opinions after his trial.

Clayton’s IQ score evokes last term’s ruling Hall v. Florida, in which the U.S. Supreme Court struck down Florida’s strict IQ limit of 70 or below for executions after the state denied a competency hearing to an inmate with an IQ of 71. In Hall, the Court required states to consider other factors when assessing mental competency, including the margin of error in IQ tests. Judge Stith emphatically suggested her colleagues’ decision violated the Supreme Court’s ruling and, by extension, the Constitution.

Here, as in Hall, Cecil Clayton most recently has posted an IQ score of 71. The majority does not deny that if Clayton had a score of 66, or some other score below 70, he would be entitled to a hearing as to his intellectual disability. But, because his score is 71, it says he does not. This is exactly what the Supreme Court in Hall disallowed! (Emphasis original)

Even if Clayton gets a hearing, though, there’s no guarantee of its result. Although the U.S. Supreme Court forbade executions of people with intellectual disabilities in its 2002 ruling in Atkins v. Virginia, the justices left the task of defining “intellectual disability” to the states. Missouri’s death-penalty statute requires that an inmate’s intellectual disability be “manifested and documented before eighteen years of age.” Clayton was 32 years old when the sawmill injury destroyed part of his brain.

Since brain injuries don’t travel backwards in time, the statute’s requirement seems to foreclose the possibility that, under Missouri law, a person can become intellectually disabled as an adult. The Missouri Supreme Court ruled against Clayton’s claim accordingly. “The school records and other evidence provided by Clayton in this case show that he was of average intelligence—or better—before age 18, and this continued at least until his brain injury in 1972,” the court explained in its ruling. “Accordingly, he cannot be ‘intellectually disabled’ as that term is defined in Missouri law.”

This logic baffled the three dissenters. Atkins, Judge Stith wrote, “does not depend on when an intellectual disability manifested, but on whether an intellectual disability exists.” Clayton’s lawyers argue that the Missouri law clashes both with Supreme Court precedents and with the purpose of the death penalty itself. “Executing someone who, but for the age of onset of his disabilities, is ‘Atkins ineligible’ for execution does not serve any legitimate goals of capital punishment,” Clayton’s lawyers told the high court.

This case is more than an exercise in procedural technicalities. Both supporters and opponents of the death penalty have a stake in ensuring that it is carried out fairly and meticulously. Refusing to assess the mental competence of an inmate who obviously meets the threshold for evaluation makes a mockery of the judicial process. Cecil Clayton is not the only party to this case whose competence is now in question.