An Alabama Death Row inmate set to die next month by suffocating on nitrogen gas has settled his case with the state prison system.

Alan Miller, 59,is set to die on Sept. 26 at William C. Holman Correctional Facility in Atmore. The prison is the only facility in the state with an execution chamber and is where most death row inmates are housed.

In a filing on Monday, Miller’s lawyers said they had entered into a “confidential settlement agreement” with the Alabama Department of Corrections and other state officials.

They asked the lawsuit be dismissed.

The execution, if it goes off as scheduled, would be just the second execution using nitrogen hypoxia in the country. The first was also done in Alabama, when the state put Kenneth Smith to death in January.

A prison spokesperson told AL.com that the execution is still scheduled for next month. “Everything is still set to proceed barring any additional legal barriers,” said Kelly Betts.

Controversy followed that execution, after Smith thrashed and exhibited seizure-like movements in the minutes before he lost consciousness.

State officials have argued that Smith held his breath at the beginning of his execution, delaying the nitrogen entering his body.

But Miller’s lawyers argued that the state doesn’t offer any proof for their claims and the state “hang(s) their hat exclusively on the self-serving testimony of a witness who claims to have remembered Mr. Smith’s oxygen levels nearly seven months after the execution.”

The execution team captain didn’t write down those oxygen levels, according to Miller’s lawyers, nor tell anyone about them on the night of the execution.

“In fact, evidence in the record suggest that the witness could not even see the levels from his position in the execution chamber, and the execution log from Mr. Smith’s execution… undercuts (the state’s) entire argument,” said the filing.

In a deposition earlier this summer, Miller said he has no intention of holding his breath or resisting his execution, but he’s worried the state will fail at securing his gas mask because they’re “incompetent.”

“I don’t think ya’ll know what you’re doing,” Miller told a state attorney during the deposition. “And these guys can’t even open a cell door sometimes. They’re keystone cops is basically what they are.”

In an earlier filing in federal court, Miller’s attorneys said Alabama Attorney General Steve Marshall’s office and its deputy, James Houts, are “responsible for training the execution team on how to carry out a nitrogen hypoxia execution.”

Miller said he’s open to having the gas mask fitted to his face prior to his September execution, but only if a doctor, medical professional or third party appointed by a federal judge does the fitting.

The settlement agreement comes just one day before the court was set to hold a hearing in-person at the downtown Montgomery federal courthouse.