A forensic scientist testified in Arlington County Circuit Court yesterday that a pair of wire cutters found in the Fairfax County home of GOP activist Kevin Sabo was the tool used last March to cut the brake lines on his ex-girlfriend's car, causing it to crash.

An analysis made with a sophisticated microscope revealed that the wire cutters seized by police left unique markings on the severed steel brake lines from the 1997 Volkswagen Jetta, said Julien J. Mason Jr., a director at the Northern Virginia Regional Forensic Lab.

"This tool cut these brake lines--and no other," testified Mason, holding up Exhibit 9-A for the jury.

Mason's testimony came on the opening day of Sabo's trial on an attempted malicious wounding charge. Sabo, 38, is accused of cutting the brake lines on the car of his ex-girlfriend, Heather Lawrence, 28, on March 17. Sabo, a lawyer, resigned his appointment to Virginia's Commonwealth Transportation Board in the wake of the allegations.

The trial opened with both sides describing a volatile, sometimes violent eight-month relationship that began when Sabo was still living with his wife and daughter. He and Lawrence met at a lobbying firm in the District, where he was general counsel and she was a media relations specialist.

Deputy Commonwealth's Attorney Theo Stamos told jurors that Lawrence, who was not injured in the crash, was so terrified that someone was trying to kill her that she had a security system installed at her Arlington town house, wore a panic button around her neck that could activate the alarm and rarely went out alone.

Lawrence had broken off her relationship with Sabo the day before her brakes were cut, and she suspected he might have done it, Stamos said. Determined to find out for sure, Lawrence had police install a tape recorder on her phone so she could record their conversations, the prosecutor said.

During a four-hour taped phone conversation several weeks after the crash, Sabo admitted to Lawrence that he had tampered with her car, Stamos told the jury. "I did something to your car," Stamos said Sabo told Lawrence. "I don't know what--but I did something to your car."

Defense attorney A. Strode Brent tried to portray Lawrence as "more of the aggressor" of the two, saying she punched Sabo, yanked the prescription glasses off his face and threw his cell phone into a brick wall during their stormy relationship.

As Lawrence took the stand, Brent hammered at her, saying that any statements his client had made to her were the result of her lies and an "accumulation of threats," particularly that she would tell his now ex-wife about their affair and damage his relationship with his daughter.

Lawrence agreed that she had often lied to Sabo in their phone conversations in an attempt to extract an admission from him. Under Brent's questioning, she broke down crying on the stand as she denied the lawyer's suggestions that she was after Sabo's money.

"I have been through hell to get to this point," said Lawrence, whose sobs brought a brief recess. "I want justice. Period. No money."

Lawrence said that as she was driving to work March 17, she approached the busy intersection of Brookside Drive and Washington Boulevard and realized in horror that she couldn't stop the car.

"My foot went completely to the floor," Lawrence said. "I had no brakes. I just turned the car hard left and hit a fence."

Testimony will resume today in a trial that was expected to last as long as four days. Sabo faces up to 10 years in prison if convicted.