Alabama is asking a federal appeals court to let it proceed with a lethal injection this week, arguing there is no evidence to corroborate the prisoner’s claim that he selected another execution method.

Alabama Attorney General Steve Marshall on Tuesday asked the 11th U.S. Circuit Court of Appeals to lift an injunction blocking the execution of Alan Miller. Miller was sentenced to die after being convicted of killing three people in a 1999 workplace shooting. The lethal injection was scheduled for Thursday until it was blocked by a judge.

Miller testified that in 2018 he turned in paperwork selecting nitrogen hypoxia as his execution method, and his lawyers maintain the state lost the form. U.S. District Judge R. Austin Huffaker Jr. issued a preliminary injunction blocking the state from by any means other than nitrogen hypoxia.

The state argued in the court filing that there is no reliable evidence that Miller elected nitrogen hypoxia. “Miller offers no evidence aside from a self-serving affidavit,” lawyers for the state wrote.

Nitrogen hypoxia is a proposed execution method in which death would be caused by forcing the inmate to breathe only nitrogen, thereby depriving him or her of the oxygen needed to maintain bodily functions. Nitrogen hypoxia has been authorized as an execution method in Alabama, Oklahoma and Mississippi, but no state has attempted to put an inmate to death by the untested method.

When Alabama approved nitrogen hypoxia as an alternative execution method in 2018, state law gave inmates a brief window to designate it as their execution method.

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

Trial testimony indicated that Miller believed the men were spreading rumors about him, including that he was gay. A defense psychiatrist hired found that Miller suffered from delusions and severe mental illness, according to court documents, but he also said Miller’s condition wasn’t bad enough to use as a basis for an insanity defense under state law.