Ex-Classmate Recalls Thornton’s Troubles : Courts: Penalty-phase witnesses say convicted killer displayed antisocial behavior as far back as kindergarten.

Even as a 5-year-old, convicted Thousand Oaks killer Mark Scott Thornton was a misfit.

That was the testimony Monday from one of Thornton’s kindergarten classmates and several other defense witnesses as the third week of Thornton’s death-penalty hearing got under way.

Thornton--convicted in December of fatally shooting Westlake nurse Kellie O’Sullivan last year--had problems getting along with others from the start and constantly picked fights just for the attention, testified former classmate Ian Horn, now 20.

“It didn’t seem like he knew how to act around people,” said Horn, looking at Thornton for the first time in more than a dozen years.

The Superior Court jury is deciding whether Thornton should live or die for killing the 33-year-old nurse, who prosecutors say was kidnaped in Thousand Oaks and shot while on her knees in the Santa Monica Mountains.

Defense attorneys changed their focus Monday from the defendant’s deprived upbringing to his poor school performance and antisocial childhood behavior.

The defense contends Thornton suffered brain damage at birth and, as a result, is an immature adult who cannot control his impulses.

His condition worsened, they suggested Monday, when he was bitten in the face by a dog at age 5, just a few months before he was to enter kindergarten.

In connection with a lawsuit over the dog-biting incident, Thornton was examined by psychologist Brian Jacks. By the time he saw the defendant, Jacks testified, Thornton was already “a troubled boy in troubled circumstances.”

*

Jacks told the jury that Thornton’s mother was nice but undependable, constantly breaking appointments for treatment of her son. In fact, Jacks said, he did not prescribe medicine for Thornton’s condition because he did not think he could trust the defendant’s mother with drugs.

The mother, Markita Sarrazin, has testified that she was drug-addicted when Thornton was a young boy.

Jacks told the jury that the dog bite caused Thornton to have nightmares and wet his bed.

In his opinion, Jacks said, Thornton suffered from an attention deficit hyperactive disorder, a form of depression marked by inattention, impulsive actions and restlessness.

Jacks said the disheveled boy left an impression with him.

“I remember him because he was a rather cute little boy who looked like Dennis the Menace, and he was getting into that same kind of trouble too,” said Jacks.

At school, Thornton would often hang around the fence encircling the playground instead of joining in the games with other children, said Paul Horn, the father of his classmate.

Horn lived across the street from Ivanhoe Elementary and kept watch over the campus when school was not in session. He often watched the kids play during recess.

“I felt that Mark really wasn’t part of the play group,” Horn said. “I felt concern for Mark first. Then I felt sorry for him as I saw him alone more and more.”

*

Others described Thornton as skittish and nervous.

Even in the third grade, “Mark would sometimes whine and act like a 4- to 5-year-old,” said Josephine Walker, his special-education teacher.

Eventually, however, Thornton seemed to mature as school officials diagnosed his special needs and gave him individual attention, Walker said.