An Alabama man, found guilty of a 1988 murder, was executed by nitrogen gas on Tuesday night, marking the sixth such execution in the country.

Gregory Hunt, aged 65, was declared dead at 6:26 p.m. in a prison located in southern Alabama, as confirmed by officials. His execution was one of four planned across the United States this week. Hunt had been convicted of capital murder for the death of 32-year-old Karen Lane, which took place on August 2, 1988, in the Cordova apartment she shared with another woman in Walker County.

The execution method involves forcing an inmate to breathe pure nitrogen gas, depriving them of the oxygen needed to stay alive.

While strapped to a gurney with a mask covering his entire face, Hunt did not utter any final words but instead seemed to gesture a thumbs-up and a peace sign. The flow of gas started sometime after 5:55 p.m., though the precise moment was uncertain.

At 5:57 p.m. Hunt briefly shook, gasped and raised his head off the gurney. He let out a moan at about 5:59 p.m. and raised his feet. He took a series of four or more gasping breaths with long pauses in between, and made no visible movements after 6:05 p.m.

The shaking movements and gasps were similar to previous nitrogen executions in Alabama. The state says the movements are expected, but critics say they show that the execution method does not provide a quick death.

“What I saw has been consistent with all the other nitrogen hypoxia executions. There is involuntary body movement,” Alabama Corrections Commissioner John Hamm said.

Hunt had dated Lane for about a month. Prosecutors said that after becoming enraged with jealousy, he broke into Lane’s apartment and sexually abused her and beat her to death, inflicting 60 injuries on her body. Jurors convicted him in 1990 and recommended a death sentence by an 11-1 vote.

Several of Lane’s relatives witnessed the execution, Hamm said. The family said in a statement that the night was not about Hunt’s life but rather the “horrific death of Karen Sanders Lane, whose life was so savagely taken from her.” They said Hunt showed her no mercy in 1988.

“This is also not about closure or victory. This night represents justice and the end of a nightmare that has coursed through our family for 37 years,” the family said.

Alabama Attorney General Steve Marshall called the execution “a long-overdue moment of justice.”

“Karen was a young woman whose life was stolen in the most brutal and dehumanizing way imaginable,” Marshall said, adding, “Gregory Hunt spent more time on death row than Karen spent alive.”

Hunt was among the longest-serving inmates on Alabama’s death row. He told The Associated Press last month that finding religion in prison helped him get “free of my poisons and demons” and that he tried to help other inmates. He led a weekly Bible class since 1998, he said.

“Just trying to be a light in a dark place, trying to tell people if I can change, they can too … become people of love instead of hate,” he said.

The U.S. Supreme Court denied Hunt’s request for a stay about three hours before the execution began. Hunt argued that prosecutors misled jurors about the evidence of sexual abuse, a claim the Alabama attorney general’s office called meritless.

Hunt declined to have a dinner meal. On the day of his execution, he had a lunch tray that included bologna, black-eyed peas, carrots and fruit punch, prison officials said.

The Rev. Jeff Hood, a death penalty opponent who worked with Hunt, expressed sadness over his execution.

“Greg Hunt was my friend. I am devastated that Alabama saw fit to kill him,” Hood said.

Last year Alabama became the first state to carry out an execution with nitrogen gas. The method has now been used in six executions — five in Alabama and one in Louisiana.

Hunt selected nitrogen over the other options, lethal injection or the electric chair, before Alabama developed procedures for the method.

Hunt’s was one of two executions carried out Tuesday in the country. In Florida, Anthony Wainwright, 54, died by lethal injection for the April 1994 killing of 23-year-old Carmen Gayheart, a nursing student and mother of two young children, in Lake City.