An Alabama inmate has filed a lawsuit against the state to avoid being the second person to be executed using nitrogen gas citing 'cruel and unusual punishment.'

Alan Eugene Miller, 57, had survived an attempted execution by lethal injection in 2022, but is now set to be the second to die by nitrogen gas.

His execution date is set for September 22 at William C. Holman Correctional Facility in Escambia County, but his attorneys are fighting using the method after a murderer subjected to nitrogen gas 'writhed in agony' for 22 minutes on January 25.

Kenneth Smith was left shaking and convulsing as he was put to death, leading Miller's legal team to claim using death by nitrogen gas on their client would be a 'cruel and unusual punishment.'

The attorneys have also claimed that the state is trying to 'silence' miller, who spoke out against the lethal injection after the failed attempt - which they have called a violation of his free speech and due process of rights.

'Rather than address these failures, the State of Alabama has attempted to maintain secrecy and avoid public scrutiny, in part by misrepresenting what happened in this botched execution,' the lawyers wrote.

They said Alabama was unable to conduct such an execution 'without cruelly superadding pain and disgrace, and prolonging death.'

A spokeswoman for Alabama Attorney General Steve Marshall did not immediately respond to a text message seeking comment on the lawsuit.

Despite Smith's clearly agonizing and torturous death, Alabama's Attorney General Steve Marshall vowed to keep using nitrogen gas to execute inmates.

Marshall filed a motion in February asking the court to allow the Alabama Department of Corrections to execute Alan Eugene Miller, who has been on death row since 2000 for murdering two co-workers and a former co-worker at separate locations in 1999.

Alabama has also offered to aid other states seeking to carry out executions using nitrogen gas, a method Alabama called 'the most painless and humane method of execution known to man' but one that human rights groups have condemned as cruel and torturous.

What occurred last night was textbook,' Marshall said after Smith's execution, contrasting allegations from many, including Smith's spiritual advisor who said it was 'torture' and the 'worst thing' he had ever seen.

'When they turned the nitrogen on, he began to convulse, he popped up on the gurney over and over again, he shook the whole gurney,' spiritual advisor Jeff Hood, who was in the chamber, said immediately after the execution.

Marshall said of the 165 inmates on Alabama's death row, 43 prisoners have opted to be executed via nitrogen hypoxia over lethal injection when their time comes.

'We'll definitely have more nitrogen hypoxia executions in Alabama,' he concluded.

In filings before the execution, the state argued that 'the experts agree that nitrogen hypoxia is painless because it causes unconsciousness in seconds.'

Marshall reportedly conceded that this was not exactly how it unfolded Thursday night as it took longer than anticipated, but said it was difficult to discern the timing due to difficulty knowing when the nitrogen began to flow.

'It's interesting to see the attorney general say that everything went consistent with plans that they laid out,' Hedgepeth told MSNBC.

'We saw him begin violently shaking, thrashing against the straps that held him down.

'This was the fifth execution that I've witnessed in Alabama, and I've never seen such a violent execution or a violent reaction to the means of execution.'