Texas on Tuesday plans to execute a convicted murderer whose hopes are pinned to two appeals, including one that challenges the state's planned use of a secretly-made drug like those used in Oklahoma's botched execution two weeks ago.

Robert James Campbell, 41, would be the first U.S. inmate put to death since the botched execution of Clayton Lockett, whose vein collapsed during his lethal injection, prompting prison officials to halt the execution. He later died of a heart attack.

This handout photo provided by the Texas Department of Criminal Justice shows Robert Campbell. (AP Photo/Texas Department of Criminal Justice)

Like Oklahoma, Texas won't say where it obtains the drugs it uses in executions, saying it needs to protect the identity of the producer to protect it from possible threats by death penalty opponents. Unlike Oklahoma, which used a three-drug combination in Lockett's execution, Texas uses a single dose of the sedative pentobarbital to kill inmates.

Campbell's attorneys say Lockett's failed execution proves what many inmates have been arguing since states turned to made-to-order drugs: that the drugs put the inmates at risk of being subjected to inhumane pain and suffering.

"This is a crucial moment when Texas must recognize that death row prisoners can no longer presume safety unless full disclosure is compelled so that the courts can fully review the lethal injection drugs to be used and ensure that they are safe and legal," said Maurie Levin, one of Campbell's attorneys.

The state's attorneys, though, say Campbell's claims are speculative and fall "far short" of demonstrating a significant risk of severe pain.

"The Constitution does not require the elimination of all risk of pain," argued Ellen Stewart-Klein, an assistant Texas attorney general.

Campbell's execution would be the eighth this year for Texas, which kills more inmates than any other state, and the fourth in recent weeks to use the compounded pentobarbital.

Texas invoked confidentiality in late March when it obtained a new supply of pentobarbital to replace a stock that had reached its expiration date.

Campbell's appeals moved Monday to the 5th U.S. Circuit Court of Appeals after they were rejected by state courts and lower federal courts.

In the appeal that challenges the secrecy surrounding the drug, U.S. District Judge Keith Ellison said he couldn't overturn 5th Circuit decisions in similar cases, but he urged the higher court to reconsider its rulings, saying they seemed "to shield crucial elements of the execution process from open inquiry."

Another appeal before the 5th Circuit holds that Campbell isn't mentally competent enough to execute because he has a 69 IQ, and courts have generally set a 70 IQ as the minimum threshold.

Campbell was convicted of capital murder for the January 1991 slaying of a 20-year-old Houston bank teller, Alexandra Rendon. She was abducted while putting gas into her car, robbed, raped and shot.

"This was not a shoot and rob and run away," Rendon's cousin, Israel Santana, said. "The agony she had to go through. ... It works me up."

Rendon, who had been making wedding plans, was buried wearing her recently purchased wedding dress.