McALESTER, Okla. (AP) — Oklahoma executed a man Thursday for the 1998 stabbing death of a prison cafeteria worker, the state’s first lethal injection following a six-year moratorium.

John Marion Grant, 60, is the first inmate to be executed since a series of flawed executions in 2014 and 2015. Grant was serving a 130-year prison sentence for several armed robberies when witnesses say he dragged prison cafeteria worker Gay Carter into a mop closet and stabbed her 16 times with a homemade shank. He was sentenced to die in 1999.

Oklahoma moved forward with Grant’s lethal injection after the U.S. Supreme Court, in a 5-3 decision, lifted stays of execution that were put in place on Wednesday for Grant and another death row inmate, Julius Jones, by the 10th U.S. Circuit Court of Appeals.

The state’s Pardon and Parole Board twice denied Grant’s request for clemency, including a 3-2 vote this month to reject a recommendation that his life be spared.

Oklahoma has historically had one of the nation’s busiest death chambers, but a series of problematic lethal injections in 2014 and 2015 led to a de facto moratorium. Richard Glossip was just hours away from being executed in September 2015 when prison officials realized they received the wrong lethal drug. It was later learned the same wrong drug had been used to execute an inmate in January 2015.

The drug mix-ups followed a botched execution in April 2014 in which inmate Clayton Lockett struggled on a gurney before dying 43 minutes into his lethal injection — and after the state’s prisons chief ordered executioners to stop.

While the moratorium was in place, Oklahoma moved ahead with plans to use nitrogen gas to execute inmates, but ultimately scrapped that idea and announced last year that it planned to resume executions using the same three-drug lethal injection protocol that was used during the flawed executions. The three drugs are: midazolam, a sedative, vecuronium bromide, a paralytic, and potassium chloride, which stops the heart.

Oklahoma prison officials recently announced that they have confirmed a source to supply all the drugs needed for seven executions that are scheduled to take place through March.

“Extensive validations and redundancies have been implemented since the last execution in order to ensure that the process works as intended,” the Department of Corrections said in a statement.

More than two dozen Oklahoma death row inmates are part of a federal lawsuit challenging the state’s lethal injection protocols, arguing that the three-drug method risks causing unconstitutional pain and suffering. A trial is set for early next year.

Grant and five other death row inmates were dismissed from the lawsuit after none of them selected an alternate method of execution, which a federal judge said was necessary. But a three-member panel of the Denver-based 10th U.S. Circuit Court of Appeals determined that the inmates did identify alternative methods of execution, even if they didn’t specifically check a box designating which technique they would use. The panel had granted stays of execution on Wednesday for Grant and Jones, whose lethal injection is set for Nov. 18.

Grant and his attorneys did not denied that he killed Carter, but argued that key facts about the crime and Grant’s troubled childhood were never presented to the jury. They maintained that Grant developed deep feelings for Carter and was upset when she fired him after he got in a fight with another kitchen worker.

“Jurors never heard that Mr. Grant killed Ms. Gay Carter while in the heat of passion and despair over the abrupt end of the deepest and most important adult relationship of his life,” his attorneys wrote in his clemency application.

Carter’s daughter, Pam Carter, who also worked at the prison and was there the day her mother was killed, rejected the idea that her mother and Grant had anything more than a professional relationship and urged state officials to move forward with the execution.

“I understand he’s trying to save his life, but you keep victimizing my mother with these stupid allegations,” she told the Pardon and Parole Board this month. “My mother was vivacious. She was friendly. She didn’t meet a stranger. She treated her workers just as you would on a job on the outside. For someone to take advantage of that is just heinous.”