Alabama executed a man using nitrogen gas for the second time on Thursday.

Alan Eugene Miller, 59, was pronounced dead at 6:38 p.m. local time at a south Alabama prison, The Associated Press reported.

He was convicted of killing three men—Lee Holdbrooks, Christopher Scott Yancy and Terry Jarvis—in workplace shootings in 1999.

“I didn’t do anything to be in here,” Miller said in his final words, the AP reported. His words were at times muffled by the blue-rimmed gas mask that covered his face from forehead to chin.

Miller asked his family and friends to “take care” of someone, but it was not clear whose name he said.

Alabama had tried to execute Miller via lethal injection in 2022, but the state called it off after being unable to connect an IV line. He initially challenged the nitrogen gas protocol but dropped his lawsuit in August after reaching a settlement with the state. The terms of the settlement were not disclosed.

He was one of five inmates executed over the past week, including Emmanuel Littlejohn who was also put to death on Thursday in Oklahoma. Their deaths brings the U.S. to 1,600 executions since the death penalty was reinstated by the U.S. Supreme Court in 1976, according to the Death Penalty Information Center, despite support for the death penalty declining nationwide over the past two decades.

The nitrogen gas method used to put Miller to death involves placing a respirator gas mask over the inmate’s face so that they breathe pure nitrogen gas and are deprived of oxygen and die.

Alabama first used the method to put Kenneth Smith to death in January. The method has been described as inhumane by some human rights groups.

On Thursday, Miller shook and trembled on the gurney for about two minutes, with his body at times pulling against the restraints, the AP reported, followed by about six minutes of periodic gulping breaths before he became still.

In a news conference after the execution, Alabama Department of Corrections Commissioner John Hamm said the movements were anticipated.

“That was nothing we did not expect,” Hamm said, explaining the nitrogen gas flowed for 15 minutes. “Everything went according to plan and according to our protocol.”

Alabama Attorney General Steve Marshall said the execution “went as expected.”

“Although the methods have changed over the years, it remains the judgment of the State of Alabama that some crimes are so horrific as to warrant the ultimate punishment. In Alabama, we will not deny justice to the victims of heinous murders,” Marshall said in a statement.

“Tonight, despite misinformation campaigns by political activists, out-of-state lawyers, and biased media, the State proved once again that nitrogen hypoxia is both humane and effective. Miller’s execution went as expected and without incident.”

But witnesses contradicted the state’s version of events.

“I was a witness for Alabama’s execution of Alan Miller by nitrogen gas tonight,” Lauren Gill, a writer for Bolts magazine, wrote on X, formerly Twitter. “Again, it did not go as state officials promised. Miller visibly struggled for roughly two minutes, shaking and pulling at his restraints. He then spent the next 5-6 min intermittently gasping for air.”

Marshall’s description of Smith’s execution in January as “textbook” also differed from witness accounts, with advocates saying he had exhibited clear signs of pain and suffering.

One witness described how Smith began “thrashing against the straps” as the gas flowed and his head and body violently jerked back and forth for several minutes.

Update 9/27/24, 3:30 a.m. ET: This article has been updated with additional information.