ANGOLA, La. — Louisiana used nitrogen gas to put a man to death Tuesday evening for a killing decades ago, marking the first time the state has used the method as it resumed executions after a 15-year hiatus.

Jessie Hoffman Jr., 46, was pronounced dead at 6:50 p.m. at the Louisiana State Penitentiary, authorities said, adding the nitrogen gas had flowed for 19 minutes during what one official characterized as a “flawless” execution.

Witnesses to the execution said Hoffman appeared to involuntarily shake or had “some convulsive activity.” But the three witnesses who spoke — including two members of the media — agreed that, based on the protocol and what they learned about the execution method, nothing seemed out of the ordinary.

Witness Gina Swanson, a reporter with WDSU, described the execution from her viewpoint as “clinical” and “procedural.” She said there was nothing that occurred during the process that made her think, “Was that right? Was that how it was supposed to go?”

Hoffman declined to make a final statement in the execution chamber. He also declined a final meal.

It was the fifth time nitrogen gas was used in the U.S. after four executions by the same method — all in Alabama. Three other executions, by lethal injection, are scheduled this week — in Arizona on Wednesday and in Florida and Oklahoma on Thursday.

Hoffman was convicted of the murder of Mary “Molly” Elliott, a 28-year-old advertising executive who was killed in New Orleans. At the time of the crime, Hoffman was 18 and has since spent much of his adult life at the penitentiary in rural southeast Louisiana, where he was executed Tuesday evening.

After court battles earlier this month, attorneys for Hoffman had turned to the Supreme Court in last-ditch hopes of halting the execution. Last year, the court declined to intervene in the nation’s first nitrogen hypoxia execution, in Alabama.

Hoffman’s lawyers had unsuccessfully argued that the nitrogen gas procedure — which deprives a person of oxygen — violates the Eighth Amendment’s prohibition on cruel and unusual punishment. The man’s lawyers, in a last-ditch appeal, also argued the method would infringe on Hoffman’s freedom to practice religion, specifically his Buddhist breathing and meditation in the moments leading up to death.

Louisiana officials maintained the method is painless. They also said it was past time for the state to deliver justice as promised to victims’ families after a decade and a half hiatus — one brought on partly by an inability to secure lethal injection drugs.

The Supreme Court voted 5-4 in declining to step in.

Hours earlier at a hearing Tuesday, a 19th Judicial District Court Judge Richard “Chip” Moore also declined to stop the execution. He agreed with the state’s lawyers who had argued the man’s religion-based arguments fell under the jurisdiction of a federal judge who had already ruled on them, according to local news outlets.

Under the Louisiana protocol, which is nearly identical to Alabama’s, officials had earlier said Hoffman would be strapped to a gurney before a full-face respirator mask fitted tightly on him. Pure nitrogen gas was then pumped into the mask, forcing him to breathe it in and depriving him of the oxygen needed to maintain bodily functions.

The protocol called for the gas to be administered for at least 15 minutes or five minutes after the inmate’s heart rate reaches a flatline indication on the EKG, whichever is longer.

Two media witnesses to Tuesday’s execution said Hoffman was covered with a gray plush blanket from the neck down. In the chamber with Hoffman was his spiritual advisor. Ahead of the execution and after the curtains closed to the viewing room, witnesses said they could hear Buddhist chanting.

The gas began to flow at 6:21 p.m. and Hoffman started twitching, media witnesses said. His hands clenched and he had a “slight head movement.” Swanson said she closely watched the blanket over Hoffman’s chest area and could see it rise and fall, indicating that he was breathing. She said his last visible breath appeared to be at 6:37 p.m. Shortly after, the curtains between the chamber and witness viewing room closed. When they reopened, Hoffman was pronounced dead.

Seth Smith, chief of operations at the Louisiana Department of Public Safety and Corrections, witnessed the execution and also acknowledged Hoffman’s movements. Smith, who has a medical background, said he perceived the convulsions to be an “involuntary response to dying” and that Hoffman appeared to be unconscious at the time.

Each inmate put to death using nitrogen in Alabama had appeared to shake and gasp to varying degrees during their executions, according to media witnesses, including an Associated Press reporter. Alabama state officials said the reactions were involuntary movements associated with oxygen deprivation.

Alabama first used nitrogen gas to put Kenneth Eugene Smith to death last year, marking the first time a new method had been used in the U.S. since lethal injection was introduced in 1982.

Alabama, Louisiana, Mississippi and Oklahoma specifically authorize execution by nitrogen hypoxia, according to records compiled by the Death Penalty Information Center. Arkansas was added to the list on Tuesday.

Seeking to resume executions, Louisiana’s GOP-dominated Legislature expanded the state’s approved death penalty methods last year to include nitrogen hypoxia and electrocution. Lethal injection was already in place.

On Tuesday, Arkansas Gov. Sarah Huckabee Sanders signed legislation allowing executions using nitrogen gas, making hers the fifth state to adopt the method. Arkansas currently has 25 people on death row.

Over recent decades, the number of executions nationally has declined sharply amid legal battles, a shortage of lethal injection drugs and waning public support for capital punishment. That has led a majority of states to either abolish or pause carrying out the death penalty.

On Tuesday afternoon, a small group of execution opponents held a vigil outside the rural southeast Louisiana prison at Angola, where the state’s executions are carried out. Some passed out prayer cards with photos of a smiling Hoffman and planned a Buddhist reading and “Meditation for Peace.”

Louisiana Attorney General Liz Murrill said she expects at least four people to be executed this year in the state. Following Hoffman’s execution, she said justice had been delayed for far too long and now Hoffman ”faces the ultimate judgement, the judgement before God.”