Montgomery, Alabama - Alabama is due to execute Alan Eugene Miller by nitrogen gas later this year after the state attorney general's office settled a lawsuit in the case.

Miller's case argued that the protocol for his planned execution by nitrogen hypoxia violated his constitutional protections against cruel and unusual punishment.

The lawsuit was dismissed with prejudice, meaning it cannot be brought forward again, while the terms remain confidential.

"The resolution of this case confirms that Alabama’s nitrogen hypoxia system is reliable and humane," Alabama's Republican Attorney General Steve Marshall said in a statement.

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"Miller’s complaint was based on media speculation that Kenneth Smith suffered cruel and unusual punishment in the January 2024 execution, but what the State demonstrated to Miller’s legal team undermined that false narrative. Miller’s execution will go forward as planned in September."

In January, Smith became the first known person in the nation to be put to death with nitrogen gas, a method human rights advocates have denounced as a form of torture.

A previous attempt to execute Miller by lethal injection failed in 2022 as officials had trouble accessing his veins at the time.

Miller's lawyers afterward fought for execution by nitrogen gas but filed their complaint after reports that Smith struggled and suffered during his execution.

Miller and his lawyers were requesting several changes to the protocol, including a larger mask and the presence of medical experts.

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Miller has been convicted in the August 5, 1999, murders of his former co-workers Lee Holdbrooks, Scott Yancey, and Terry Lee Jarvis.

A forensic psychiatrist testified that Miller had mental illness and was suffering from a delusional disorder, leading him to believe the three had been spreading rumors about him.

MIller's execution is expected to take place between September 26 and 27.