MONTGOMERY, Alabama (AP) — A divided Alabama Supreme Court said the state can execute an inmate with nitrogen gas, a method that has not previously been used carry out a death sentence.

The all-Republican court in a 6-2 decision Wednesday granted the state attorney general’s request for an execution warrant for Kenneth Eugene Smith. The order did not specify the execution method, but the Alabama attorney general indicated in filings with the court that it intends to use nitrogen to put Smith to death. The exact date of the execution will be set later by Alabama Governor Kay Ivey.

The decision moves Alabama closer to being the first state to attempt an execution with nitrogen gas, although there is likely to be additional litigation over the proposed new execution method. Three states — Alabama, Oklahoma and Mississippi — have authorised nitrogen hypoxia as an execution method but no state has attempted to use it.

Smith was one of two men convicted in the 1988 murder-for-hire slaying of Elizabeth Sennett in Alabama’s Colbert County.

“Elizabeth Sennett’s family has waited an unconscionable 35 years to see justice served. Today, the Alabama Supreme Court cleared the way for Kenneth Eugene Smith to be executed by nitrogen hypoxia,” Alabama Attorney General Steve Marshall wrote. “Though the wait has been far too long, I am grateful that our capital litigators have nearly gotten this case to the finish line.”

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

Lawyers for Smith had urged the court to reject the execution request.

“The state seeks to make Mr Smith the test subject for the first ever attempted execution by an untested and only recently released protocol for executing condemned people by the novel method of nitrogen hypoxia,” Smith’s attorneys wrote in a September court filing.

Under the proposed method, the inmate would be forced to breathe only nitrogen, depriving them of oxygen needed to maintain bodily functions and causing them to die. Nitrogen makes up 78 per cent of the air inhaled by humans and is harmless when inhaled with oxygen. While proponents of the new method have theorized it would be painless, opponents have likened it to human experimentation.

The state unsuccessfully attempted to put Smith to death 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.

Smith’s attorneys previously accused the state of trying to move Smith to “the front of the line” for a nitrogen execution in order to moot Smith’s lawsuit challenging lethal injection procedures.

Chief Justice Tom Parker and Justice Greg Cook dissented in Wednesday’s decision.

Prosecutors said 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. The slaying, and the revelations over who was behind it, rocked the small north Alabama community. Her husband killed himself a week later. The other man convicted in the slaying was executed in 2010.