UPDATE: The execution was halted on Tuesday afternoon by a federal appeals court. More here.

Two weeks after a botched execution in Oklahoma, which left an inmate writhing in pain and drew worldwide scrutiny, Texas is scheduled to execute convicted murderer Robert James Campbell.

The execution in Texas will be the eighth in the state this year, the most of any state. In the wake of the botched execution, Texas defended its lethal injection protocol, which kills inmates using one drug (pentobarbital) rather than the three-drug mix used in Oklahoma.

“The current Texas protocol has been in place since July 2012 – and since then, 33 executions have been carried out without incident,” Jerry Strickland, a spokesman for the state’s attorney general Greg Abbott, said in an e-mail.

Campbell is set to be executed for murdering Alexandra Rendon in 1991. Rendon, a 20-year-old bank teller, was abducted by Campbell and an accomplice, Leroy Lewis, while she was getting gas. She was robbed and raped before Campbell shot and killed her.

Update, 2:54 p.m.: Attorneys for Campbell filed an appeal and a stay motion with the Supreme Court on Tuesday, citing the secrecy surrounding the source of the drug Texas plans to use for the execution.

“The extreme secrecy which surrounded lethal injection in Oklahoma prior to Mr. Lockett’s execution led directly to disastrous consequences….. Unless the courts demand that Texas proceed with a commitment to transparency and accountability, there is an unacceptable risk that other prisoners will be subjected to the torturous death suffered by Mr. Lockett,” Maurie Levin, one of Campbell’s attorneys, said in a statement.

Back to original post: Executions in Texas have been carried out recently using a supply of pentobarbital obtained from a compounding pharmacy that has not been identified. States have scrambled to deal with a shortage of drugs needed for lethal injections, as objections from European officials and companies have caused some states to run out of the drugs used in executions.

Attorneys for Campbell have argued that in the wake of the Oklahoma execution, it’s “unthinkable” for Texas to hide the source of the drug that will be used in his execution.

“It is deeply shameful that Texas has more interest in protecting the identity of the supplying compounding pharmacy than they do in ensuring that they carry out executions in a humane manner,” Maurie Levin, an attorney for Campbell, said in a statement last week.

Campbell’s attorneys have also said that he is mentally impaired, with attorney Robert C. Owen calling it “an outrage” that Texas had not properly considered this factor.

If Texas executes Campbell, he would become the 21st person executed in the U.S. The execution would be the first since Oklahoma attempted to kill Clayton Lockett on April 29. Lockett, who was convicted of murder and numerous other charges, was set to die by lethal injection. But after he was declared unconscious, Lockett began grimacing and trying to move off of the gurney; the technician saw that his vein collapsed, according to an official timeline released by the state, and the execution was called off. He died of a heart attack 43 minutes after the execution began.

Lockett’s execution was supposed to be followed later that same night by the execution of Charles F. Warner, who was convicted of raping and murdering an 11-month-old. After the botched execution, Oklahoma Gov. Mary Fallin (R) announced a two-week stay of execution for Warner, which would have pushed his execution to Tuesday night. Warner’s execution was postponed again when Fallin announced that she had ordered an independent review of her state’s execution procedures, as Fallin said that Warner’s execution will be delayed until the review is completed.

The head of Oklahoma’s Department of Corrections said that the state’s executions should be delayed indefinitely, while the state’s attorney general later agreed that Oklahoma should delay its next execution for six months.

President Obama called the botched Oklahoma execution “deeply troubling” and said it highlighted significant problems with how the death penalty is utilized in the country.

Since 1976, Texas has executed 515 people, the most of any state by a very wide margin, according to the Death Penalty Information Center. (The state with the second-highest number of executions, Oklahoma, has killed 111 people.) There are three executions scheduled in Texas for later this year, one in August and two in September.