RENO, Nev. (AP) — Lawyers for a four-time convicted murderer in Nevada are trying to persuade a federal judge to grant a temporary stay of execution for the man who’s scheduled to become the first inmate put to death in the state in 15 years.

Public defenders for Zane Michael Floyd are scheduled to go before a judge in Las Vegas Monday afternoon to argue over the constitutionality of a never-before-used sequence of drugs that prison officials plan to use at the state-sanctioned killing tentatively scheduled next month.

They say lethal injection would subject him to cruel and unusual pain and that Floyd prefers safer alternatives, including a firing squad or a single dose of a barbiturate.

Defense lawyers also filed another appeal with the Nevada Supreme Court last week that says the Clark County district attorney’s office should be disqualified from helping prosecute the case because of a conflict of interest on the part of two deputy district attorneys who also serve as members of the Nevada Senate.

Meanwhile, the manufacturer of one of the drugs says the state obtained it from them illegally. Lawyers for Hikma Pharmaceuticals told Nevada’s attorney general last week they want the state to return 50 vials of the anesthetic ketamine.

Aides to Attorney General Aaron Ford provided a copy of the letter Monday to The Associated Press but said they had no comment on the demand to return the drugs.

Floyd, 45, was convicted of killing four people and wounding a fifth in a 1999 shotgun attack at a Las Vegas grocery store.

A death warrant for Floyd is scheduled to be issued July 9, with an exact execution date to follow. It would be the first execution in Nevada since 2006 when Daryl Mack was given a lethal injection for a 1988 rape and murder in Reno.

A team of deputy federal public defenders representing Floyd has asked U.S. District Judge Richard Boulware II to slow the case to allow enough time to examine the effects of the lethal drugs that would be used — including the powerful opioid fentanyl, the sedative ketamine, heart-stopping potassium chloride and perhaps a muscle paralytic called cisatracurium. The state’s execution plan was made public a little more than two weeks ago.

The last death row inmate in Nevada who had been scheduled to be executed was Scott Dozier.

In 2017 and 2018, battles over the effects of three-drug procedure that the state Department of Corrections picked for Dozier — including fentanyl and cisatracurium — prompted judges to call off the execution. Dozier killed himself in the Ely state prison in January 2019.

Prosecutors said in recent court filings the Nevada Department of Corrections has provided the court with undisputed medical and pharmaceutical evidence establishing the execution will not result in unconstitutional pain or suffering — “indeed, it is likely to result in very minimal to no pain.”

Floyd’s lawyers say the state wrongly maintains that those are not legitimate alternatives because Nevada law provides only for lethal injection and the Department of Corrections has been unable to procure a barbiturate.

They said the Supreme Court has made it clear that an inmate seeking to identify an alternative method of execution is not limited to choosing among those presently authorized by a particular state’s law. They said both of Floyd’s proposed alternatives are well-established in other jurisdictions.

Mississippi, Oklahoma, South Carolina and Utah currently authorize execution by firing squad, they said. Texas, Georgia and the U.S. government have recently used pentobarbital in carrying out executions.

Hikma Pharmaceuticals said in its cease-and-desist letter to the state last week that the ketamine it produces is meant for life-saving purposes and long has opposed use of its products for capital punishment. It said the drug has never been used in an execution and notes the company won a federal court order in 2018 that concluded the Nevada Department of Corrections had resorted to “subterfuge” when it similarly, illegally acquired ketamine for such purposes.

“This is not Hikma’s first rodeo with NDOC on this issue,” its lawyer wrote on Thursday. “It is nothing less than shocking and embarrassing for the state of Nevada.”