A federal appeals court granted a condemned Texas man’s request for a stay of execution hours before he was scheduled for execution on Tuesday evening.

The stay, issued by the United States Court of Appeals for the Fifth Circuit in New Orleans, comes after lawyers for inmate Robert Campbell said they found two previously undisclosed IQ test results supporting their claim that Mr. Campbell is mentally handicapped. The state had withheld both IQ scores when the defense first raised the issue of Campbell’s possible mental disabilities in an unsuccessful appeal in 2003, according to the Fifth Circuit's opinion.

Campbell’s “lifelong mental retardation was not proven until new evidence, long hidden by prosecutors and the Texas Department of Criminal Justice, very recently came to light,” said Robert Owen, one of Campbell’s lawyers, in a statement.

“Given the state’s own role in creating the regrettable circumstances that led to the Fifth Circuit’s decision today, the time is right for the State of Texas to let go of its efforts to execute Mr. Campbell, and resolve this case by reducing his sentence to life imprisonment,” said Mr. Owen.

A 2002 Supreme Court ruling protects people with mental disabilities from execution. The stay allows Campbell’s legal team to file a new appeal to throw out his death sentence.

The incident is the latest to raise questions about how the death penalty is being administered in the United States:

In recent months, two executions using untested concoctions of lethal-injection drugs appear to have resulted in extreme pain; Oklahoma and Ohio have delayed executions as a result.

A recent study suggested that 4 percent of inmates sentenced to death in the US are innocent.

A panel of legal experts last week issued a high-profile report critiquing several aspects of how capital punishment is practiced in the US, including concerns that it is carried out on the mentally disabled.

In the Campbell case, the Texas Court of Criminal Appeals denied Campbell’s appeal in 2003, arguing that he was not mentally handicapped based on Campbell’s score of 84 on the lone IQ test the court believed he had taken, according to the Fifth Circuit opinion. The test had been given in 1990, when Campbell was doing time for another offense, the state had said.

But, during the last few weeks, Campbell’s new defense team found two other IQ scores: One, administered by prison officials in 1992, put his IQ at 71; the other, given to him as a child and obtained by the district attorney’s office in Houston in 1991, put his IQ at 68, according to the opinion.

The Texas Department of Justice had withheld the first score from Campbell’s lawyers, even when a lawyer asked in a letter ahead of the 2003 appeal if such a test existed, the opinion says. The DA’s office also did not turn over Campbell’s IQ score from school, even as it was opposing Campbell’s appeal by saying that his record would be unable to prove he was mentally disabled, according to the opinion.

The Fifth Circuit also noted in its opinion that the Texas Department of Justice was unable to supply any details about the 1990 IQ test on which Campbell had scored an 84, including “whether such a test had been administered at all.”

“It is regrettable that we are now reviewing evidence of intellectual disability at the eleventh hour before Campbell’s execution,” wrote James Dennis, a Fifth Circuit judge. “However, from the record before us, it appears we cannot fault Campbell or his attorneys, present or past, for the delay.”

The Fifth Circuit’s decision came just hours after it denied a separate appeal from Campbell arguing that the state was violating Campbell’s right to an execution free from cruel and unusual punishment by refusing to name the pharmacy where it had purchased its lethal injection drugs.

Campbell would have been the first inmate to be put to death in the US since the bungled execution of Clayton Lockett in Oklahoma, which also sourced its drugs from an unnamed pharmacy. Oklahoma has since delayed all executions in the state for at least six months.