A federal judge has ordered Alabama to stop being vague and to provide a firm answer by Thursday evening on whether the prison system is prepared to use the untested execution method of nitrogen hypoxia during an execution next week.

U.S. District Judge R. Austin Huffaker, Jr. set a Sept. 22 deadline for the state to file an affidavit, or declaration, on whether the state could try to execute inmate Alan Miller by nitrogen hypoxia if the use of lethal injection is blocked. The order came after the state dangled the possibility of becoming the first state to attempt an execution with nitrogen hypoxia during a court hearing on Monday.

Nitrogen hypoxia is a proposed execution method in which the inmate is forced to breathe only nitrogen, depriving him or her of the oxygen required to maintain bodily functions. It is legal in three states — Alabama, Oklahoma, and Mississippi — but it has never been used.

The state provided “vague and imprecise statements regarding the readiness and intent to proceed with an execution by nitrogen hypoxia on September 22, 2022,” according to Huffaker.

The judge asked the state on Monday if it was prepared to use the method during Miller’s execution. A state attorney responded that it was “very likely” that nitrogen hypoxia would be used next week, but that the final decision would be made by the state prison commissioner.

“On or before September 15, 2022 at 5:00 p.m. CDT,” the judge wrote in a Tuesday order, “the defendants shall file an affidavit or declaration of Commissioner John Q. Hamm, Attorney General Steve Marshall, or other appropriate official with personal knowledge, definitively setting forth whether or not the Defendants can execute the Plaintiff by nitrogen hypoxia on September 22, 2022.”

Miller is attempting to prevent his scheduled execution by lethal injection by claiming that prison staff misplaced paperwork when he returned in 2018 and chose nitrogen hypoxia as his execution method.

Miller testified on Monday that he is afraid of needles, so he signed a form requesting nitrogen hypoxia as his method of execution. He stated that he placed the form in his cell door tray for an officer to retrieve it. The state said there is no evidence to corroborate his claim.

Miller, a delivery truck driver, was convicted in the 1999 workplace shootings in suburban Birmingham that killed Lee Holdbrooks, Scott Yancy, and Terry Jarvis. Miller shot Holdbrooks and Yancy at one location before driving to another to shoot Jarvis, according to evidence.

Miller suffered from severe mental illness, according to a defense psychiatrist, but his condition was not severe enough to support an insanity defense under state law.

In 2018, Alabama lawmakers approved legislation authorizing nitrogen hypoxia as an alternative execution method, though lethal injection would continue to be the primary method of carrying out death sentences. Inmates had a limited time to choose nitrogen as their method of execution under state law. Several inmates chose nitrogen.

The state has revealed little about the new execution method. Last year, the Alabama Department of Corrections informed a federal judge that it had completed a “system” for using nitrogen gas but did not describe it.