Alabama is one step closer to carrying out the first execution by nitrogen hypoxia, an untested execution method that has attracted controversy since it was approved in the state in 2018.

On Wednesday, a federal judge ruled that the execution of 58-year-old Kenneth Eugene Smith could go forward later this month, dismissing arguments that the execution would make him a “test subject” in an unproven execution method. The move appears to be a last-ditch effort to halt Smith’s death, as Smith’s lawyers had previously fought to allow him to be executed by nitrogen hypoxia instead of lethal injection.

“There is simply not enough evidence to find with any degree of certainty or likelihood that execution by nitrogen hypoxia under the Protocol is substantially likely to cause Smith superadded pain short of death or a prolonged death,” wrote Judge R. Austin Huffaker Jr. “It could, in a highly theoretical sense, but only if a cascade of unlikely events occurs. Or it may well be painless and quick. Execution by nitrogen hypoxia is novel.”

Smith was sentenced to death for the 1988 murder-for-hire of Elizabeth Sennett. Smith and another man were convicted of taking $1,000 each from Sennett’s husband to murder her. Smith’s accomplice was executed in 2010.

In November 2022, Alabama tried to execute Smith by lethal injection but abandoned the attempt after prison officials were unable to successfully place an IV line by the midnight deadline. In response to Smith’s failed execution and two other similarly failed and botched execution attempts, Republican Alabama Gov. Kay Ivey announced a temporary moratorium on executions in the state. However, the moratorium was lifted in February 2023 after an opaque internal investigation.

In the meantime, Smith and his lawyers argued that he should be able to choose execution by nitrogen hypoxia instead. While the method was approved by the Alabama Legislature in 2018, it has yet to be used to actually execute someone. In theory, the inmate would be placed in a gas chamber with a respirator-type mask on. The percentage of oxygen in the air flowing through the mask would be slowly replaced with more and more nitrogen, until the mask only produced nitrogen, suffocating the inmate. 

After a significant legal fight, Smith won the right to be executed by nitrogen hypoxia in August 2023. However, with his execution date set, his lawyers reversed course in a last-minute attempt to save his life, arguing that the state’s execution protocol is flawed and likely to lead to an extended, painful death.

“The evidence establishes that executing Mr. Smith by nitrogen hypoxia using the Protocol would subject him to a substantial risk of serious harm,” Smith’s lawyers wrote in December. “Specifically, ADOC’s plan to deliver nitrogen gas to Mr. Smith through a mask that is placed over his face subjects him to a substantial risk that (1) oxygen will infiltrate the mask, which could leave Mr. Smith in a persistent vegetative stroke, cause him to have a stroke, or to experience the sensation of suffocation, and (2) he will asphyxiate on his own vomit.”

However, this latest attempt seems unlikely to save Smith’s life. Since ending its execution moratorium, Alabama has expressed particular zeal for executing death-row inmates—having killed two inmates in the past six months.