McALESTER, Okla. (AP) _ With a glance toward the family members of some of his victims, Richard Alford Thornburg, Jr., apologized for murdering three people shortly before he was executed Tuesday at the Oklahoma State Penetentiary.

``I just want to say I'm sorry for all the pain I've caused,'' said Thornburg, who was strapped to a gurney. ``I'm truly ashamed of my actions.

``I wish I could take it back.''

Some of the victims' family members witnessed the execution from behind one-way glass to a room overlooking the death chamber.

A lethal cocktail of drugs started to flow into Thornburg's arm at 6:16 p.m., causing him to exhale deeply before his breath hitched one time. His eyes remained open as a doctor declared him dead at 6:20 p.m.

Five people, including Thornburg's sister, wife and two brothers-in-law also witnessed his execution, but prison officials did not release their names. The two women cried quietly as they watched Thornburg strain to lift his head and look at them.

Earlier Tuesday, Thornburg was served his last meal _ a chicken dinner, potato wedges, apple pie and a Pepsi from Kentucky Fried Chicken.

Thornburg was convicted of the Sept. 28, 1996, shooting deaths of James Donald Poteet, 51; Terry Lynn Shepard, 39; and Keith Alan Smith, 24. Two other men also were convicted of murder in the case.

The three killings occurred at Poteet's house in Alex, which was set on fire.

The defendants held a fourth man, Marvin Matheson, at gunpoint and forced him to shoot Donald Brent Scott, who survived his wounds, prosecutors said.

``Although he was shot in the chest, fortunately for us, Donald Scott managed to crawl out of the burning home and survived,'' said Grady County Assistant District Attorney Bret Burns, who prosecuted Thornburg. ``If he hadn't survived, nobody would have believed this story.''

Scott lived next door to Poteet, and Burns said the defendants kidnapped Scott, Shepard and Smith from Scott's house so there would be no eyewitnesses to the crime.

Glenn Anderson also was convicted of first-degree murder in the case and sentenced to death. His appeal is pending with the 10th U.S. Circuit Court of Appeals.

Co-defendant Roger Embry was convicted and received one life sentence and two sentences of life without the possibility of parole.

During Thornburg's trial, defense attorneys presented testimony that Thornburg had brain damage and was subject to blackouts during bouts of heavy drinking.

Besides three murder counts, Thornburg also was convicted of shooting with intent to kill, first-degree arson and two counts of kidnapping.

Family members of the victims did not speak to the media.

However, in a letter to the clemency board signed by Keith Smith's mother, Ann Smith of Chickasha wrote that she and her husband, Carl Smith, felt robbed by their son's death.

``One week before he died, he came by and I hugged him when he left,'' she wrote. ``That was the last time I saw my son, the last time I could see the mischief in his eyes or the confidence that comes from being 24 (years old) and your whole life is ahead of you.

``Every year at that time, I am so sad and lost just wishing I could hold him one more time.''

Oklahoma has executed 159 men and three women at the Oklahoma State Penitentiary since 1915. There are currently 90 men and one woman awaiting death sentences in Oklahoma.

The last execution took place on Aug. 11, 2005, when Kenneth Eugene Turrentine was put to death for a 1994 murder in Tulsa.

John Boltz, 74, is scheduled to die June 1 for the 1984 murder of his stepson, Doug Kirby, 23, in Pottawatomie County.