Prosecutors Say Killer Was School Bully, Troublemaker : Crime: At sentencing hearing for convicted murderer Mark Scott Thornton, team denies defense claim that youth was abused, had learning disorder.

Rebutting weeks of sympathetic defense testimony, prosecutors suggested Monday that convicted killer Mark Scott Thornton failed to succeed in school because he was disruptive and unmotivated--not because he has a learning disorder.

To support their contention, prosecutors put on the witness stand a series of school officials who described Thornton as often unruly, defiant and truant in the 10th grade.

Thornton, who was convicted in December of murdering Westlake nurse Kellie O’Sullivan, in his school days taunted and bullied students who suffered physical disabilities or other problems, they testified.

The jury in Superior Court is hearing evidence to determine whether Thornton should be sentenced to death or life in prison without parole in the slaying of O’Sullivan, who was shot at a remote location in the Santa Monica Mountains after being kidnaped in Thousand Oaks.

Defense attorneys, who wrapped up four weeks of testimony Thursday, asked the jury to spare Thornton’s life. They say he was neglected and abused as a child and that he suffers a learning disorder that made school nearly impossible for him to complete.

Thornton, who moved to Thousand Oaks with his family in 1992, dropped out of high school that same year.

Prosecutors acknowledge that his home life was less than ideal--his mother and stepfather testified that they used drugs most of the time while rearing him. But prosecutors say that school officials gave Thornton more than enough attention and that he failed to complete his education because he was lazy and hard to get along with.

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One of the first witnesses Monday as the prosecution rebuttal began was Anita Dacles, Thornton’s 10th-grade English teacher at Herbert Hoover High School in Glendale. Dacles said Thornton was in a special-education English class in which she provided him with all the one-on-one attention he needed to succeed.

Thornton did not seem interested in passing her class, Dacles said.

“A lot of leeway has been given to him, a lot of chances,” she testified.

Thornton often showed up late to class, would sit down for five or 10 minutes and then leave, Dacles said.

He wound up failing the class, she said, but not because she did not try to help him pass.

“I told him that even if he does minimal work, I would pass him,” Dacles testified.

Richard W. Saunders, also a special-education teacher, said the defendant repeatedly taunted a physically disabled classmate who used a wheelchair.

He also often made fun of another student who had a persistent body odor, Saunders said.

“Mark was a difficult kid to deal with, yes,” testified Kevin Welsh, the Hoover vice principal in charge of campus discipline.

Welsh said Thornton repeatedly had to be disciplined for offenses ranging from throwing paper and mocking teachers to bullying classmates and generally defying authority.

Once, after being told not to bring a beeper to school, Thornton was suspended when a pager he carried went off during a class, Welsh said. Thornton worked for a pager company as a courier, officials said.

Welsh said he found himself spending an inordinate amount of time disciplining Thornton--even for minor infractions.

“Any time Mark came in, it was not something that was going to be simple,” the vice principal said. “It was going to be long.”