The Supreme Court on Monday agreed to review the death sentence of a man whom lawyers claim is intellectually disabled, in a case that could decide how states administer the death penalty.

“We welcome the Supreme Court's decision to review the standard Texas has been wrongfully using to determine intellectual disability and eligibility for execution,” said Karen Clifton, executive director of the Catholic Mobilizing Network. The organization is working with the U.S. bishops’ conference to end the use of the death penalty in the U.S.

“It is important to protect the most vulnerable from this type of punishment but we look forward to the day when the death penalty is declared unconstitutional once and for all,” Clifton continued.

The case, Moore v. Texas, is a challenge to the death sentence of Bobby James Moore, convicted in 1980 of robbing a grocery store and killing an employee, and convicted again in 2001 on a retrial. His lawyers say he is intellectually disabled by today’s medical standards.

The Supreme Court, in its 2002 decision Atkins v. Virginia, had ruled that the death penalty for mentally retarded persons violated the Eighth Amendment’s prohibition of cruel and unusual punishment. However, the Court left the question of determining a convict’s intellectual capacity up to the states.

Moore won in a state habeas court, which found that he was intellectually disabled and therefore unfit for the death penalty.

However, Texas’ criminal appeals court then ruled that he should be judged by the medical standards of when he had been sentenced in his 2001 retrial, since the state’s legislature had not mandated that more recent guidelines be followed. Texas had followed 1992 standards from the then-American Association of Mental Retardation, by which Moore was deemed fit for the death penalty.

In their petition for the Supreme Court to hear the case, Moore’s lawyers claimed that “applicable medical standards for diagnosing intellectual disability have changed since that time.”

They cited a state habeas court that in 2014 had determined that his “mean fullscale IQ score of 70.66 is within the range of mild mental retardation as recognized by the American Association on Mental Retardation.” They added that “review is necessary to ensure that Moore — and many others like him — are not unlawfully executed.”

According to Robert Dunham, executive director of the Death Penalty Information Center, Moore’s case is not an isolated one.

“There’s no question that states continue to execute people who have intellectual disability. It’s unconstitutional to do so, but they continue to do so,” he told CNA.

Some states have controversial methods of determining a criminal’s intellectual capacity, according to the Catholic Mobilizing Network. Louisiana relies on elected judges to ultimately determine the question. States like Texas and Florida do not abide by the most recent medical standards to deem someone unfit for the death penalty.

Georgia made headlines for multiple recent executions of men whom lawyers claimed had IQs of around 70, the threshold for determining mental retardation. The state also executed a Vietnam War veteran in 2015 who reportedly had PTSD. Georgia is the only state to require defendants to “prove ‘mental retardation’ beyond a reasonable doubt,” according to the Death Penalty Information Center.

In Hall v. Florida in 2014, the U.S. Supreme Court overruled the Florida Supreme Court, after it decided that someone with an IQ of 71 — one point above the threshold for mental retardation — could be eligible for the death penalty.

The problem, Dunham said, is that there are three “prongs” used to determine one’s capacity, and IQ score is only part of the process. Furthermore, he added, someone’s IQ score is a “range” and not an exact determination. Studies have shown that various factors can affect the IQ score on tests, particularly those that have been in use for a while.   “When the IQ score can be the difference between life and death, setting 70 as an IQ cutoff will make it so that some people will not be diagnosed with intellectual disability simply because the year in which they took the test,” Dunham said.

In their amicus brief for the 2000 death penalty case McCarver v. State of North Carolina, the United States Catholic Conference quoted from the Texas Catholic bishops, who in 1999 had spoken out against the death penalty, but specifically the execution of the intellectually disabled.

“Mentally retarded persons by definition have sub-average intellectual functioning with concurrent deficits in socially adaptive behavior,” the bishops stated. “That is not to say such persons cannot tell right from wrong or should not be held responsible for criminal behavior. However, the death penalty is the most extreme sanction available to the state, and is therefore reserved for offenders who have the highest degree of blameworthiness for an extraordinarily aggravated crime.”

“How can an individual who by definition is significantly intellectually impaired ever meet the highest standard of blame required for such a penalty?” they asked.