Judge Imposes Death Sentence on Nurse’s Killer : Courts: Victim’s 6-year-old son is among family members who take the stand to ask the court to order capital punishment.

Mark Scott Thornton, who abducted and killed a Westlake nurse during a 1993 carjacking, was sentenced Monday to death during a hearing in which the victim’s 6-year-old son pleaded with a judge to end the killer’s life.

“All I wanted to say was how I feel about what happened to my mom. It was a very bad thing,” a composed Cliff O’Sullivan Jr. told a hushed Ventura County courtroom, bringing some spectators to tears.

“All I think is that what the bad guy did to my mom should happen to him,” said the boy, who could barely see over the witness stand. “ . . . It’s really sad for my family, ‘cause she was one of the greatest mothers I’ve met.”

Thornton, 20, who will be California’s youngest Death Row inmate, bowed his head and avoided making eye contact with the child.

A jury in December convicted Thornton of first-degree murder and the special circumstance that the crime was committed during a robbery and a kidnaping. The panel recommended the death sentence in March.

According to court testimony, Thornton abducted 33-year-old Kellie O’Sullivan outside a Thousand Oaks shopping plaza the afternoon of Sept. 14, 1993. He drove her up winding roads into the Santa Monica Mountains, where he shot her once in the chest and twice in the back.

Stealing her new Ford Explorer, Thornton drove to Simi Valley and had the name of his ex-girlfriend tattooed on his shoulder. He then kidnaped the girl, 16-year-old Stephanie Campbell, and held her captive before his arrest five days later at a casino in Nevada.

O’Sullivan’s decomposed body was found in a desolate mountain grotto 12 days after her disappearance. The crime outraged the Thousand Oaks community, and more than 200 volunteers joined the search for the missing nurse.

Thornton’s trial, which lasted six months and involved more than 125 witnesses, was one of the biggest criminal cases in recent Ventura County history.

But after Monday’s sentence, prosecutors and defense attorneys still disagreed on the outcome.

Deputy Public Defender Susan R. Olson said the jury lost its objectivity because O’Sullivan was an unlikely crime victim.

“She became sort of the totem figure as the ideal, middle-class woman: a white female, a nurse and a mother,” said Olson, who unsuccessfully tried to persuade the judge to reduce Thornton’s sentence to life in prison without parole.

“If this [murder] had happened to someone in inner-city Los Angeles, my guess is that this would have been plea-bargained for life in prison without parole,” Olson said.

Thornton choked back tears as a lawyer pleaded with the judge to spare the defendant’s life. But Thornton, who has said his lawyers kept him from testifying against his will, did not ask Monday to make a statement.

Deputy Dist. Atty. Peter D. Kossoris said the murder was premeditated and called Thornton a con artist and liar. He told the judge that Thornton has a “cowardly, cold, depraved attitude.”

Superior Court Judge Charles R. McGrath agreed that the circumstances of the crime were too heinous to merit any penalty other than death.

“That death is warranted is overwhelmingly supported by the evidence,” the judge said.

Outside court, O’Sullivan family members exchanged celebratory hugs with five jurors who returned to court for the sentencing.

“He had a blatant, complete and total disregard for human life,” said juror Jesse Wilson. “He killed just to satisfy his own selfish needs. He gave absolutely no mercy to her, and I can’t find one reason to give him mercy.”

In addition to the boy, O’Sullivan’s mother, ex-husband and the former husband’s cousin gave statements about the impact her death has had on them.

The mother said her daughter was not perfect, but would not have ever left her son alone. “I lost my daughter in a coldblooded act of murder,” said Sharlene Cunningham.

Outside court, Cliff O’Sullivan said he was pleased with the sentence. “It went exactly how I hoped it would,” he said.

Times correspondent Andrew D. Blechman contributed to this report.