ATMORE, Ala. — An Alabama man, implicated in a 1993 murder involving the horrific act of burning a man over a $200 drug debt, faced execution on Thursday through nitrogen gas.

Anthony Boyd, aged 54, was declared deceased at 6:33 p.m. at the William C. Holman Correctional Facility, as reported by officials. Alabama, which adopted nitrogen gas as an execution method last year, used it for Boyd, who was sentenced to death for his involvement in the murder of Gregory Huguley in Talladega County. Prosecutors revealed that Huguley was set ablaze after failing to pay for $200 worth of cocaine.

In his final moments, Boyd professed his innocence and condemned the criminal justice system.

“I didn’t kill anybody. I didn’t participate in killing anybody,” Boyd asserted.

He further added, “There can be no justice until we change this system.” Boyd expressed affection for those continuing the fight for justice and concluded with, “Let’s get it.”

The execution seemed to last longer than previous ones using nitrogen gas, but the state did not disclose when the gas was initiated.

At about 5:57 p.m. Boyd clenched his fist, raised his head off the gurney slightly and began shaking. He then raised his legs off the gurney several inches. At about 6:01 p.m. he began a long series of heaving breaths that lasted at least 15 minutes, before becoming still. The curtain closed to the execution chamber at 6:27 p.m. The prison commissioner said the gas is kept flowing for five minutes after monitoring shows the inmate no longer has a heartbeat.

A prosecution witness at Boyd’s trial testified as part of a plea agreement and said that Boyd taped Huguley’s feet together before another man doused him in gasoline and set him on fire. Defense lawyers said he was at a party on the night Huguley was killed and the plea deal testimony was unreliable.

A jury convicted Boyd of capital murder during a kidnapping and recommended by a vote of 10-2 that he receive a death sentence.

Alabama Attorney General Steve Marshall said in a statement that the state “remains steadfast in its commitment to uphold the law and deliver justice for victims and their families.”

“For more than 30 years, Boyd sought to delay justice through endless litigation, yet he never once presented evidence that the jury was wrong,” Marshall said.

Boyd had been on Alabama’s death row since 1995. He was the latest chair of Project Hope to Abolish the Death Penalty, an anti-death penalty group founded by men on death row.

Alabama began using nitrogen gas last year to carry out some executions. The method uses a gas mask strapped over the inmate’s face to replace breathable air with pure nitrogen gas, causing the person to die from lack of oxygen.

Nationally, the method has now been used in eight executions: seven times in Alabama and once in Louisiana.

The state and Boyd’s spiritual adviser gave conflicting accounts of what happened in the execution chamber.

The Rev. Jeff Hood stood by Boyd as he died. He was also at the first nitrogen gas execution.

“This is the worst one yet,” Hood said. “I think they are absolutely incompetent when it comes to carrying out these executions.” He said Alabama had promised nitrogen was a “quick, painless, easy form of execution and this is by far nothing anywhere close to that.”

Hood said he believed Boyd planned to try to communicate through leg movements. Hood said he believed “some level of consciousness, in my opinion, for at least 16 minutes.”

Alabama Corrections Commissioner John Hamm said he believed Boyd’s shaking and other movements were involuntary.

He said while the execution took longer than previous ones, it was “just a few minutes past some of the others.”

Boyd’s lawyers had asked a federal judge to halt the execution to give the method more scrutiny. A federal judge declined the request. She ruled Boyd was unlikely to prevail on claims that the method is unconstitutionally cruel.

The U.S. Supreme Court on Thursday afternoon also denied Boyd’s request to stay the execution and to instead let him die by firing squad. Justice Sonia Sotomayor authored a scathing dissent joined by Justices Elena Kagan and Ketanji Brown Jackson.

Sotomayor, citing witness descriptions of past nitrogen gas executions, wrote that there is “mounting and unbroken evidence” that the method is unconstitutional. She wrote that “allowing the nitrogen hypoxia experiment to continue” fails to protect the dignity of the nation.

Alabama has maintained that any shaking or gasping exhibited by inmates during nitrogen gas executions are largely involuntary actions caused by oxygen deprivation.