Updated

A Texas man convicted of killing a 38-year-old woman nearly two decades ago while he was on parole for a triple slaying years earlier was executed Thursday evening.

Robert Ladd, 57, received a lethal injection after the U.S. Supreme Court rejected arguments he was mentally impaired and ineligible for the death penalty. The court also rejected an appeal in which Ladd's attorney challenged whether the pentobarbital Texas uses in executions is potent enough to not cause unconstitutional pain and suffering.

Ladd was executed for the 1996 slaying of 38-year-old Vicki Ann Garner, of Tyler, who was strangled and beaten with a hammer. Her arms and legs were bound, bedding was placed between her legs, and she was set on fire in her apartment.

In his final statement, Ladd addressed the sister of his victim by name, telling her he was "really, really sorry."

"I really, really hope and pray you don't have hatred in your heart," he said, adding that he didn't think she could have closure but hoped she could find peace. "A revenge death won't get you anything," he said.

Then Ladd told the warden: "Let's ride."

As the drug took effect, he said: "Stings my arm, man!" He began taking deep breaths, then started snoring. His snores became breaths, each one becoming less pronounced, before he stopped all movement.

He was pronounced dead at 7:02 p.m., 27 minutes after the drug was administered.

Teresa Wooten, Garner's sister, said afterward that she accepted Ladd's apology and held no anger toward him.

"We hate the sin he committed. We hate the deed he committed," Wooten said. "But at the end of his life we no longer hated the man and have sympathy for his family."

Ladd came within hours of lethal injection in 2003 before a federal court agreed to hear evidence about juvenile records that suggested he was mentally impaired. That appeal was denied and the Supreme Court last year turned down a review of Ladd's case. His attorneys renewed similar arguments as his new execution date approached.

"Ladd's deficits are well documented, debilitating and significant," Brian Stull, a senior staff lawyer with the American Civil Liberties Union Capital Punishment Project, told the high court.

Kelli Weaver, a Texas attorney general, reminded the justices in a filing that "each court that has reviewed Ladd's claim has determined that Ladd is not intellectually disabled."

Ladd's lawyers cited a psychiatrist's determination in 1970 that Ladd, then a 13-year-old in custody of the Texas Youth Commission, had an IQ of 67. Courts have embraced scientific studies that consider an IQ of 70 a threshold for impairment. The inmate's attorneys also contended he long has had difficulties with social skills and functioning on his own.

Ladd also was a plaintiff in a lawsuit questioning the "quality and viability" of Texas' supply of its execution drug, pentobarbital. The Texas Attorney General's Office called the challenge "nothing more than rank speculation."

When he was arrested for Garner's slaying, Ladd had been on parole for about four years after serving about a third of a 40-year prison term for the slayings of a Dallas woman and her two children. He pleaded guilty to those crimes.