MONTGOMERY, Ala. (AP) — Alabama has set a January execution date for what would be the nation’s first attempt to put an inmate to death using nitrogen gas.

Alabama Gov. Kay Ivey on Wednesday announced a Jan. 25 execution date for Kenneth Eugene Smith using the new execution method of nitrogen hypoxia. Smith was one of two men convicted in the 1988 murder-for-hire slaying of Elizabeth Sennett in northwestern Alabama.

A divided Alabama Supreme Court last week granted the state attorney general’s request to authorize Smith’s execution. It is the responsibility of the governor to set the exact execution date.

The announcement moves Alabama closer to becoming the first state to attempt an execution by nitrogen gas, although there will likely be additional legal wrangling over the proposed method. Nitrogen hypoxia has been authorized as an execution method in Alabama, Oklahoma and Mississippi, but no state has used it.

While proponents have theorized the execution method would be painless, opponents have likened it to human experimentation.

Nitrogen makes up 78% of the air inhaled by humans and is harmless when inhaled with proper levels of oxygen. Under the proposed procedures, a mask would be placed over the inmate’s nose and mouth and their breathing air would be replaced with nitrogen, depriving them of the oxygen needed to stay alive. The nitrogen “will be administered for 15 minutes or five minutes following a flatline indication on the EKG, whichever is longer,” according to the execution protocol.

Alabama Attorney General Steve Marshall last week said the court decision had “cleared the way” for Smith’s execution by nitrogen hypoxia. He said Sennett’s family has “waited an unconscionable 35 years to see justice served.”

An attorney for Smith did not immediately return an email seeking comment.

The state tried but failed to execute Smith by lethal injection last year. The Alabama Department of Corrections called off the execution when the execution team could not get the required two intravenous lines connected to Smith.

Prosecutors say Smith was one of two men who were each paid $1,000 to kill Sennett on behalf of her pastor husband, who was deeply in debt and wanted to collect on insurance. Her husband killed himself a week later. The other man convicted in the slaying was executed in 2010.