Frank Duane Welch, 46, was pronounced dead at 6:21 p.m. after receiving a lethal mixture of drugs at the Oklahoma State Penitentiary.

Welch was executed for the death of Jo Talley Cooper, 28, of Norman, whose 1987 murder went unsolved for nearly a decade.

Welch was serving time in prison for a kidnapping when in 1997 he was linked by DNA to the killings of Cooper and Grady County resident Debra Stevens, whose nude body was found in her family's home outside Tuttle less than three months after Cooper's death.

"For the Cooper and Stevens families, there's nothing that can change the horrible thing I've done," Welch said while strapped to a gurney.

I'm truly, truly sorry for all the hurt and pain I've caused ya'll. I take full responsibility for what I've done. There's no excuse for it. There never was."

As the lethal combination of drugs flowed into Welch's arm, one of his brothers, who was in an adjacent viewing room, began having breathing problems and collapsed to the floor. Prison medical personnel attended to him, but he refused to be taken to a hospital in an ambulance, officials said.

Cooper, a Mississippi native who received a master's degree in communication at the University of Oklahoma, was three months' pregnant when she was killed. She was tied up, raped and strangled while her infant son slept in the next room.

Prosecutors believe that Welch, who worked as a cable television repairman in Norman for a short time in 1987, used his old uniform to get inside the women's homes.

Cooper's family witnessed Welch's execution. Her son, Travis Cooper, is now 21 and lives in Madison, Wis., with his father.

In a letter to the Oklahoma Pardon and Parole Board last month, he urged the board to deny clemency for Welch and wrote of the pain of growing up without his mother.

"It would be different if my mother would have died of natural causes," he wrote. "It would be different if it was God's will, but the truth is that an evil man named Frank Welch took her life.

"And the unspeakable things he did to her, my mother, is what fills me with anger, the pain, and the loneliness that I feel to this day."