Woman Testifies in Murder Trial to Seeing Man Beat His Passenger : Courts: Prosecutors say witness saw Mark Scott Thornton driving with victim before she was shot dead.

Margaret Spalding of Westlake was heading down Hampshire Road in her Mercedes last year, when a small black truck veered into her path, she testified Wednesday.

After avoiding a collision, Spalding said, she realized what was wrong: The young, dark-haired man driving the truck was punching his female passenger instead of paying attention to the road.

Prosecutors say the man was accused Thousand Oaks murderer Mark Scott Thornton.

They contend Spalding saw Thornton as he was taking 33-year-old Westlake nurse Kellie O’Sullivan to the Santa Monica Mountains, where she was shot and killed.

One of four prosecution witnesses on the seventh day of Thornton’s death penalty trial, Spalding told a Superior Court jury that the woman who was being pummeled wore a white blouse with a dark-colored sweater pulled over her shoulders, the same clothing other witnesses saw O’Sullivan wearing.

Spalding, on her way to buy items for her son’s upcoming camping trip, was driving south on Hampshire Road in the middle lane. The black truck was also headed south, in the right lane, toward Westlake Boulevard.

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Spalding noticed the man and woman arguing, she said, before the woman suddenly “made a dive toward his lap and the steering column.”

“At that time, he took his right elbow, shoved her back and punched her,” Spalding said. “He didn’t use his hand. He used his elbow.”

“Did it look like a hard blow?” questioned Deputy Dist. Atty. Peter D. Kossoris.

“It was enough to shove her up in her seat, yes.”

She could tell that tempers were flaring in the truck, Spalding testified. “He was starting to get vocal. He turned facing her and was talking to her. Not just talking, but he became upset.”

The passenger recoiled for a few seconds, started talking to the driver again and made another stab for whatever she was trying to get, Spalding testified.

According to earlier testimony, Thornton always kept his .38-caliber pistol either in his waistband or in the truck’s console.

After apparently being warned by her male driver, the woman sat back up in the passenger seat, Spalding said. But then she lunged toward him a third time.

“They struggled and the car veered all the way toward me. I was afraid I was going to get hit. He was striking her repeatedly in the midsection.”

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Spalding said she looked down for some paper to take down the truck’s license plate number. When she looked back up, the truck had turned right on Westlake Boulevard--in the direction of Mulholland Road and the Santa Monica Mountains.

She immediately told her teen-age son about the confrontation, but no one else, Spalding said. She said she didn’t know what else to do. Trying to cast doubt over Spalding’s credibility, Thornton attorney Howard J. Asher asked why she did not call the police right away.

“I had nothing to go on,” she responded. “I’m sure the Police Department is not going to go around looking for a black vehicle without a license plate number.”

Nine days later, she told her best friend about the incident because it was keeping her awake at night, she said. Her friend got her to call the police, who then made the connection between the incident and O’Sullivan, whose body was found three days later.