UPDATE: According to CNN, a stay has been granted in the scheduled execution of Robert James Campbell by the Fifth Circuit Court. Campbell had been scheduled to be put to death tonight in Texas. Campbell was convicted of a 1991 homicide.
The Court granted the stay based on the defenses clam that Mr. Campbell was intellectually disabled.
Original Report: Texas plans to put to death Tuesday a convicted rapist and murderer who, a neuropsychologist says, is "mildly mentally retarded," in the nation's first execution since a botched lethal injection in Oklahoma left an inmate writhing in pain before death.
The inmate's defense team is challenging, on a variety of grounds, the state's decision to execute him, including ineffective assistance of counsel, state misconduct, the refusal of the state of Texas to divulge the source of its execution drugs, and the man's mental capacity.
The Texas attorney general's office declined to comment, and this week the U.S. Fifth Circuit Court of Appeals denied motions for a stay. The motions cited the mental-retardation and drug-source claims.
The execution of Robert James Campbell, 41, is slated for 5 p.m. ET at the Texas State Penitentiary at Huntsville, about 70 miles north of Houston. The facility, nicknamed "Walls Unit" for its red brick facades, has hosted 876 executions since 1924.
According to court documents and the Texas Department of Criminal Justice, Campbell was involved in a string of armed carjackings in 1990 and 1991. In one incident, Alexandra Rendon, a 20-year-old Houston bank employee, was snatched from a gas station, robbed, sexually assaulted and fatally shot.
"Mr. Campbell gave Ms. Rendon's coat to his mother, and her jewelry to his girlfriend, as gifts; he also drove Ms. Rendon's car openly in his own neighborhood, and told people he had been involved in the crime," according to his application for post-conviction relief.
These facts are key, as the defense team says they indicate that "Mr. Campbell demonstrates no criminal sophistication."
Testing showed Campbell had "applied academic skills consistent with an individual midway through fifth grade," according to court documents, and while he was able to count and add change, he was inconsistent "calculating change from a purchase."
He also asked a friend for help reading a non-digital watch, and an informant told the court Campbell could not read a car's gas gauge and "always had to ask others whether there was enough fuel to get to the destination," the documents say.
Dr. Leslie Rosenstein, a clinical neuropsychologist, diagnosed Campbell with "mild mental retardation," saying his performance on recent tests was consistent with his standardized intelligence test scores when he was a child, according to court documents.
This, too is important, because Campbell's defense team alleges the Texas Department of Criminal Justice was aware of Campbell's low test scores, yet told his defense team in 2003 that his only IQ test, 13 years prior, yielded a score of 84, well above the threshold for mental retardation.
But as Judge Elsa Alcala wrote last week in her dissent to the Texas Court of Criminal Appeals' 5-4 decision, a defense team later learned the Department of Criminal Justice administered a test in 1992, on which Campbell scored a 71. Alcala described it as "a score that, after applying the standard of margin of error, would indicate mental retardation."
Had the department not "misinformed" Campbell's defense, the judge wrote, "then this court would have had IQ testing supportive of applicant's mental-retardation claim." Also influencing the dissent is that Rosenstein had deemed the 1990 test score of 84 "unreliable."
"This court should not base its decisions that determine whether a person will live or be executed based on misinformation or wholly inadequate information," Elsa concluded in her dissent.
Campbell's attorneys are also challenging the method by which Texas intends to execute Campbell.
The constitutionality of lethal injection drugs and drug cocktails has made headlines since last year, when European manufacturers -- including Denmark-based Lundbeck, which manufactures pentobarbital -- banned U.S. prisons from using their drugs in executions. Many states were left to find new drug protocols.
Campbell's defense cites in its appeal to the U.S. Supreme Court last month's botched execution in Oklahoma, in which a three-drug cocktail was used to to try to put to death convicted murderer Clayton Lockett. The provenance of the drugs was shielded by Oklahoma law. Lockett reportedly twitched, spoke and writhed in pain for about 40 minutes before dying of a massive heart attack.
Death row inmate Charles Warner was scheduled to die in Oklahoma the same day, but the execution was postponed. The Oklahoma Court of Criminal Appeals last week extended the stay until November 13.
"We are very pleased that the (attorney general) agrees at least 6 months is necessary before any execution in Oklahoma can take place, given the need for a full investigation to be conducted into Clayton Lockett's agonizing botched execution, and the Department of Corrections' own recognition that protocol revisions and extensive retraining are necessary," Warner's attorney, Madeline Cohen, said.
In Campbell's case, Texas intends to use pentobarbital. His attorneys say, however, that Texas' refusal to disclose the "source, efficacy and potency" of the drug raises issues similar to those in Oklahoma.
It's not about which drugs are used, Campbell's defense wrote in its appeal, but about the transparency of the entire process.
"What the events in Oklahoma have made clear is that the risk of torture and a clearly cruel and unusual outcome has been proved to be a very real threat when states aren't required to facilitate executions with the transparency and accountability and disclosure of the sort sought -- and denied -- in Oklahoma," the court document says.
"In short, the events in Oklahoma have made clear that the risk of inhumane executions is substantial, including in Texas."
CNN's Devon M. Sayers and Vivian Kuo contributed to this report.