Alabama is set to perform the second-ever nitrogen gas execution in the United States on Thursday, writes ABC NEWS.

Alan Eugene Miller, 59, was sentenced to death for the 1999 murders of his then-coworkers Lee Holdbrooks and Christoper Scott Yancy, and his former supervisor Terry Lee Jarvis.

Miller was to be executed in September 2022 via lethal injection, but it was called off after officials had trouble inserting an intravenous line to administer the fatal drugs and were concerned they would not be able to do so before the death warrant expired.

Prior to the botched execution, the state had considered carrying out the death sentence via nitrogen hypoxia, according to the Death Penalty Information Center (DPIC), a non-profit that provides data and analysis on capital punishment.

In November 2022, Alabama officials agreed not to execute Miller by lethal injection again but said if they made a second effort, the state would use nitrogen hypoxia as the method, the DPIC said.

In May 2024, the Alabama State Supreme Court agreed to let the Department of Corrections carry out Miller"s death sentence by nitrogen hypoxia. The execution is scheduled to take place at the William C. Holman Correctional Facility in Atmore, Alabama, with the window opening on Thursday, Sept. 25 at 12:00 a.m. ET and expiring on Friday, Sept. 27 at 6:00 a.m. ET. It comes after Alabama became the first state to execute a prisoner, Kenneth Eugene Smith, by nitrogen gas in January of this year.

Nitrogen hypoxia is the term for a means of death caused by breathing in enough nitrogen gas to deprive the body of oxygen - in this case, intended to be used as a method of execution. The protocol in Alabama calls for an inmate to be strapped to a gurney and fitted with a mask and a breathing tube. The mask is meant to administer 100% pure nitrogen, depriving the person of oxygen until they die.