HUNTSVILLE, Texas -- A federal appeals court on Tuesday granted a Texas inmate's request for a stay of execution hours before he was scheduled to die.

The Court of Appeals for the 5th Circuit in New Orleans granted the request from lawyers for the inmate, Robert James Campbell, on the grounds that his execution be stopped because of intellectual disability. The ruling was made just hours after the court refused to stop the execution on the basis of a different line of reasoning.

"I am happy. The Lord prevailed," Campbell said from a cell just outside the Texas death chamber in Huntsville. Campbell was convicted of capital murder for the 1991 slaying of Alexandra Rendon, who was abducted while putting gas in her car, robbed, raped and shot.

Campbell's lawyers said new information uncovered in state files showed that Campbell had an intellectual disability and was ineligible for execution. They said state officials withheld the results of two IQ tests given to Campbell -- a 68 when he was a child and a 71 shortly after he arrived on death row at the age of 19. Campbell is now 41.

The U.S. Supreme Court has banned the execution of those whom the law refers to as mentally retarded, and has said an IQ score of "approximately 70" indicates retardation. Campbell's lawyers had asked the Supreme Court for a stay of execution on the basis of the IQ issue,and filed a request with Gov. Rick Perry asking for a 30-day reprieve so that a separate plea of intellectual disability could be considered by the state Board of Pardons and Paroles.

"We have been presented with evidence that Campbell, who will soon be executed unless we intervene, may not constitutionally be executed," Judge James Dennis wrote for the court.

"It is regrettable that we are now reviewing evidence of intellectual disability at the eleventh hour before Campbell's scheduled execution," he wrote. "However, from the record before us, it appears that we cannot fault Campbell or his attorneys, present or past, for the delay."

Campbell's lawyers had been pursuing two arguments in trying to stop the execution. Along with the mental-disability appeal, known as an Atkins claim because of the Supreme Court's 2002 decision in the case Atkins v. Virginia, the lawyers also pursued a request based on Texas' refusal to identify the source of the compounded drug to be used in the execution chamber.

That line of defense was denied by the 5th Circuit earlier Tuesday and was pending before the U.S. Supreme Court.

Campbell would have been the first U.S. inmate executed since a botched execution in Oklahoma two weeks ago. Lawyers in that case also had challenged Oklahoma's plan to use a drug for which it would not reveal the source.

Like Oklahoma, Texas won't say where it gets its execution drugs, saying it needs to protect the producer's identity to prevent threats by death-penalty opponents.

Unlike Oklahoma, which used a three-drug combination in the April 29 botched execution of Clayton Lockett, Texas uses a single dose of the sedative pentobarbital to kill inmates.

During Lockett's lethal injection, the inmate's vein collapsed, causing him to writhe and grimace and prompting Oklahoma prison officials to halt the procedure. Lockett later died of a heart attack. The investigation is ongoing, but Oklahoma authorities have suggested the trouble started with Lockett's vein rather than the drugs.

Campbell's attorneys, however, are among several arguing that Lockett's prolonged and apparently painful death demands greater execution drug transparency. Texas' attorneys said Campbell's claims fall "far short" of demonstrating a significant risk of severe pain.

Maurie Levin, a lawyer for Campbell, said the 5th Circuit's decision Tuesday on the IQ issue "creates an opportunity for Texas to rise above its past mistakes and seek a resolution of this matter that will better serve the interests of all parties and the public."

She called on the state to reduce Campbell's sentence to life imprisonment given "the state's own role in creating the regrettable circumstances" that led to the decision.

Information for this article was contributed by Manny Fernandez and John Schwartz The New York Times and by Michael Graczyk of The Associated Press.

A Section on 05/14/2014