PHOENIX (AP) — A federal judge is considering whether to postpone the execution of an Arizona prisoner who argues the state’s death penalty procedures would violate his rights by subjecting him to unimaginable pain.

Attorneys for Frank Atwood said their client would undergo excruciating suffering if he were strapped to the execution gurney while lying on his back because he has a degenerative spinal condition that has left him in a wheelchair. Atwood is scheduled to be lethally injected Wednesday for his murder conviction in the 1984 killing of 8-year-old Vicki Hoskinson.

At a court hearing Friday, Atwood’s lawyers questioned whether the compounded pentobarbital to be used in the execution meets pharmaceutical standards and whether the state has met a requirement that the drug’s expiration date falls after the execution date. They also are challenging Arizona’s protocol for gas chamber executions.

Prosecutors say Atwood is trying to indefinitely postpone his execution through legal maneuvers.

Judge Michael Liburdi said he will likely issue an order over the weekend.

Two weeks ago, Atwood declined to choose between lethal injection or the gas chamber, leaving him to be put to death by lethal injection, the state’s default execution method.

Even though he didn’t pick the gas chamber, he is still challenging the state’s lethal gas protocol that calls for the use of hydrogen cyanide gas, which was used in some past U.S. executions and by Nazis to kill 865,000 Jews at the Auschwitz concentration camp alone. His lawyers say hydrogen cyanide gas is unconstitutional and produces agonizing levels of pain in executions.

Without explicitly saying Atwood wants to die by the gas chamber, his lawyers argue he has a right to choose between methods of execution that are constitutional and said the state should switch its lethal gas from hydrogen cyanide gas to nitrogen gas because nitrogen would produce painless deaths.

“They could do that tomorrow,” Joseph Perkovich, one of Atwood’s attorneys, said about nitrogen gas.

Arizona, California, Missouri and Wyoming are the only states with decades-old lethal-gas execution laws still on the books. Arizona, which carried out the last gas chamber execution in the United States more than two decades ago, is the only state to still have a working gas chamber.

In recent years, Oklahoma, Mississippi and Alabama have passed laws allowing executions with nitrogen gas, at least in some circumstances, though experts say it has never been done and no state has established a protocol that would allow it.

Atwood’s lawyers also said Arizona could take up executions by firing squad — a method of execution not used in the state.

Prosecutors say Atwood’s challenge is not aimed at minimizing the pain he will feel when he is put to death, but rather to delay the execution indefinitely by requesting alternative methods of execution that he knows the state is unable to provide without changes to its execution protocol and the state constitution.

Prosecutors say Atwood can alleviate pain caused by lying on his back by propping himself up with a pillow and using the tilt function on the execution table. They say he will be allowed to continue taking pain medications and will be provided a mild sedative before his execution.

Arizona prosecutors also said nitrogen gas remains untested in executions and that Atwood’s attorneys hadn’t established that nitrogen gas or a firing squad would reduce the risk of severe pain.

Jeffrey Sparks, a lawyer for the state, argued Atwood’s legal claims about lethal gas are moot, saying the execution will be carried out by lethal injection.

Authorities have said Atwood kidnapped Hoskinson, whose remains were discovered in the desert northwest of Tucson nearly seven months after her disappearance. Experts could not determine the cause of death from the remains that were found, according to court records.

Atwood maintains that he is innocent.

Last week, a federal appeals court denied a request by Atwood’s lawyers to make new arguments in a bid to overturn his death sentence.

Atwood’s lawyers have said that last summer they discovered an FBI memo describing an anonymous caller claiming to have seen the girl in a vehicle not associated with Atwood, but which could be linked to a woman. A panel of the 9th Circuit Court of Appeals said it couldn’t conclude that the disclosure of the unreported anonymous call would have had any effect on Atwood’s trial and conviction.

On Friday, Atwood’s lawyers also asked the Arizona Supreme Court to stay his execution, making similar arguments about what they said was new evidence of his innocence related to the woman.

Until last month, Arizona went almost eight years without carrying out an execution.

The hiatus has been attributed to the difficulty of securing lethal injection drugs as manufacturers refuse to supply them and to problems encountered during the July 2014 execution of Joseph Wood, who was given 15 doses of a two-drug combination over nearly two hours. Wood snorted repeatedly and gasped before he died. His attorney said the execution had been botched.

The hiatus ended on May 11 when the state executed Clarence Dixon for his murder conviction in the 1978 killing of Deana Bowdoin, a 21-year-old Arizona State University student.

Copyright © The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.