Thornton to Be Sentenced in Murder of Nurse : Relatives of the victim are expected to join the jury and prosecutors in urging the death penalty for the young killer.

A Ventura County judge is scheduled today to sentence Thousand Oaks killer Mark Scott Thornton for the carjack slaying of a Westlake nurse, whose 1993 abduction shocked the community and led a jury to recommend death for the baby-faced defendant.

In a third-floor courtroom at the county Hall of Justice, longtime Superior Court Judge Charles R. McGrath is set to decide whether Thornton deserves to die or spend the rest of his life in prison for murdering Kellie O’Sullivan, 33.

The hearing for the 20-year-old defendant, expected to last several hours, will signal the end to one of the county’s biggest murder trials in recent history.

For the first time, O’Sullivan’s relatives are expected to address the court today about the impact of her death. They were not allowed to testify during Thornton’s four-month trial. The victim’s 6-year-old son is expected to urge a death sentence for the defendant.

In March, a jury recommended death for Thornton, who drove O’Sullivan to a remote area of the Santa Monica Mountains and shot her once in the chest and twice in the back. He then stole her new Ford Explorer and kidnaped his girlfriend before his arrest five days later.

O’Sullivan’s body, still clad in her white nurse’s uniform, was found in a mountain grotto off Mulholland Highway 12 days after she was killed.

Prosecutors are joining O’Sullivan’s relatives in urging McGrath to impose the death penalty. They say O’Sullivan’s murder was particularly heinous because the young mother was kidnaped in broad daylight on Sept. 14, 1993, on her way to pick up her son from day care.

Thornton has demonstrated no remorse for his actions, argue prosecutors, who theorize that O’Sullivan was in utter terror during the half an hour or so she was held captive by the defendant.

”. . . The evidence shows a fatal chest wound was first inflicted, the second and third shots in the back were especially cowardly and heinous and show a completely cold and depraved state of mind,” a prosecution motion says.

Thornton, in interviews with The Times since the jury’s verdict, has said he prefers death over life in prison because Death Row inmates are isolated from other convicts. That way, he said, he would be safer from sexual assaults and other violence behind bars.

Defense attorneys acknowledge that Thornton committed a horrible crime. But it does not merit a death sentence, they say.

Thornton lawyers say the jury recommended death for Thornton because jurors lost their objectivity while hearing the case. The jurors developed sympathy for the family of the victim and hatred for Thornton, they say.

Deputy Public Defender Susan R. Olson said last week that McGrath should modify the jury’s verdict to life in prison because, in her view, that is the ruling the law and evidence support.

“This young man should not receive the death penalty,” Olson said. “Given the circumstances of the offense, as terrible as it was, and given his background, this is not a case that demands the death penalty.”

Thornton’s background was the major issue during the penalty phase of his trial. The defense presented evidence suggesting that Thornton may have suffered brain damage at birth, that he was a slow learner in school and that he was raised by drug-abusing parents in a dysfunctional household.

Deputy Dist. Atty. Peter D. Kossoris, who prosecuted the case, said none of those factors are reasons to spare Thornton’s life.

“The guy is in possession of his faculties and is fairly articulate,” Kossoris said in an interview. “He has an average IQ, knows right from wrong and knew what he was doing” during the murder.

As for Thornton’s age, Kossoris said it is irrelevant because he has a history of dishonesty.

“I don’t think age is a mitigating factor when you have a person who has been a liar and thief for years,” he said. He noted that Thornton initially denied that he killed O’Sullivan and also was convicted of forgery for stealing checks before the kidnaping.

Ultimately, perhaps the most important issue for McGrath to decide is whether the crime itself outweighs any of the conditions in Thornton’s life that may have led to the murder, attorneys agree.

Kossoris said it does.

“A lot of felony murders are robbery murders where the people do not plan to kill ahead of time and do it on a sudden impulse,” argued the prosecutor, who has sent three other men to Death Row. “In this case, the evidence showed that the defendant planned to kill her from the time he started driving in the mountains.”

Defense attorneys say the prosecution has not proved that contention. But they have not put forth their own theory of how the murder occurred.

Thornton has said he wanted to explain those events in court, but that his lawyers refused to let him take the stand.