McALESTER, Okla. -- When Melody Wuertz packed up her belongings in a moving truck and left Indiana for a new job in Oklahoma City, Lyle and Susie Wuertz were a little nervous about their daughter being on her own in a strange city.

Their nervousness grew when they learned Melody was involved with Jimmie Ray Slaughter, a man who'd been married three times and was more than 10 years her senior.

Their misgivings proved to be well founded.

Slaughter, who fathered a child with Melody Wuertz, was accused and ultimately convicted of shooting, stabbing and mutilating her and fatally shooting their daughter, Jessica, in their Edmond home in 1991.

On Tuesday, the Wuertzes traveled from Montgomery, Ind., to witness Slaughter's execution at the Oklahoma State Penitentiary. He was pronounced dead at 6:19 p.m. after receiving a lethal mixture of drugs.

Strapped to a gurney that was positioned parallel to the window separating the death chamber from the witnesses, Slaughter tilted his head so that he could smile at his three grown daughters.

"It's OK," he told them as they cried softly.

Slaughter maintained his innocence to the end.

"I've been accused of murder and it's not true," Slaughter said as his fiancee, whom he met while on death row, and a death penalty opponent who befriended Slaughter in prison, also looked on.

"It was a lie from the beginning. God knows it's true, my children who were with me know it's true and you people will know it's true someday. May God have mercy on your souls."

Slaughter had maintained he was in Kansas with his family when the murders occurred.

After his final statement, Slaughter exhaled deeply and closed his eyes. As the mixture entered his system through an IV in his left arm, the color left his face. His mouth and eyes were slightly open when he was pronounced dead.

"This is the end of a long nightmare," said Melody's brother Wes Wuertz, of Elizabethtown, Ky. "There's no more waiting for the next appeal. There's no wondering if a technicality will get him off."

The U.S. Supreme Court rejected a request by Slaughter's attorneys for a stay of execution earlier Tuesday. The 10th U.S. Circuit Court of Appeals denied an appeal on Monday and the Oklahoma Court of Criminal Appeals rejected an appeal for Slaughter on Thursday.

His attorney, Robert Jackson, had argued recently that new DNA evidence conducted on a hair found on one of the victims didn't connect Slaughter with the crimes, a theory that prosecutors argued during Slaughter's original trial.

Jackson also disputed an analysis of bullets found in the victims that he says were linked to Slaughter through an outdated technology called comparative bullet lead analysis.

A neuroscientist testified that Slaughter's brainwave patterns and recollection of the rooms where the bodies of Wuertz and her child were found were not consistent with someone who would have committed the crime.

Former Oklahoma County prosecutor Richard Wintory, who helped prosecute Slaughter at his original trial, discounted as nonsense the brain fingerprinting defense, calling it "snake oil."

"This is not a close case on the facts," said Wintory, who traveled from Arizona to attend the execution. "Jimmie Ray Slaughter perpetrated one of the most evil crimes that has ever blotted the peace and dignity of my home state."

For his last meal, Slaughter ate fried chicken, mashed potatoes, cole slaw, biscuits with honey butter, an apple pie, one pint of cherry ice cream and a large cherry limeade, a prison spokeswoman said.

A May 12 execution date has been set for George James Miller, 39, and May 19 for Garry Thomas Allen, 49.