Thornton’s Life Was Bleak, Witnesses Say : Trial: Drifter accused of killing nurse Kellie O’Sullivan slept in his car until it was towed away, his grandmother says.

Before Kellie O’Sullivan’s death, Mark Scott Thornton was a homeless teen-ager who slept wherever he could--in his beat-up old car and at a low-budget motel, defense witnesses testified Thursday.

The witnesses, including Thornton’s 68-year-old grandmother, described Thornton’s life as bleak and bereft of any opportunities.

The 20-year-old defendant is charged with murder and could be sentenced to the gas chamber in connection with the nurse’s death Sept. 14, 1993.

After nearly five weeks of testimony from prosecution witnesses, defense attorneys began presenting witnesses of their own on Thursday.

They seized the opportunity to put forth a defense apparently aimed at eliciting juror sympathy for their client.

Several witnesses told the jury that, before the nurse’s slaying, Thornton was a high school dropout forced to live on the streets after his parents evicted him from their Thousand Oaks home.

Despite his predicament, Thornton tried to improve his condition, the grandmother, Lois Thornton, and others said.

He sought help from a local charity that provided him with temporary relief, according to one witness. Eventually, witnesses said, he resorted to sleeping inside his 1976 Datsun B-210, comforting himself with a blanket and an afghan pillow.

But that housing arrangement was ended in October, 1992, when sheriff’s officials towed his car and ordered it stored. Lacking the money to retrieve it, Thornton moved to Oceano in San Luis Obispo County to live with his grandmother.

Deputy Dist. Atty. Peter D. Kossoris objected repeatedly to the line of questioning, but Superior Court Judge Charles R. McGrath allowed much of it.

Prosecutors say Thornton shot O’Sullivan in order to steal her Ford Explorer. He used the truck to kidnap his girlfriend before being arrested five days later. O’Sullivan’s body was found in the Santa Monica Mountains 12 days later.

Under direct examination from Deputy Public Defender Susan R. Olson, Lois Thornton gave the most detailed testimony.

She said Thornton’s mother, Markita, was unmarried when Mark Scott was born in July, 1974, but his mother married the boy’s father two years later. Lois Thornton said she helped raise her grandson and was very close to him.

After attending a meeting with her grandson in October, 1992, at the Conejo Valley School, a Thousand Oaks continuation high school, the grandmother asked Thornton to live with her. He came two weeks later, after his car had been towed away.

The grandmother did not detail Thornton’s problems at school, but testified he was “a confused young man, disillusioned” at the time.

That Thanksgiving, she said, they ate a free dinner at the Veterans Hall in Pismo Beach. On Christmas Day, they were fed at a church dinner for the needy. The church gave Thornton his only gift: a hand towel and some toiletries, she said.

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She said when she tried to enroll Thornton in school in San Luis Obispo, school district officials said it did not have a program “suitable for his needs.” Thornton had been a special-education student, according to court testimony.

Lois Thornton said her grandson left her home in February, 1993, having lived there three months.

She visited him on Labor Day, 1993, when he was renting a room in a Thousand Oaks home, about two weeks before O’Sullivan’s death. During that visit, he pulled a gun from under his mattress and showed it to her, Lois Thornton said.

Asked by defense attorney Olson if she could recall what the gun looked like, the grandmother’s abrupt response drew laughter: “Yes. A gun.”

Thornton, however, did not laugh. He wiped tears from his face.

When shown the murder weapon under cross-examination, Lois Thornton said it could be the same gun she saw that day.