The trip from Montgomery County toward her home in Great Falls that pleasant summer night began as a routine drive, Marna Plaia recalled yesterday. But it soon descended into chaos when a man stepped in front of her sport-utility vehicle on River Road near Potomac and said he needed help.

"He began waving his arms and physically blocked my car," Plaia, 32, testified in Montgomery Circuit Court. "I got my window down, and he told me to get out of the car, and I said: 'No, my kids. I have kids.' "

Carl E. Jones yanked open the driver's door of her 2002 Mercedes and pulled her out of the vehicle, Plaia told a jury. She landed on the ground, and Jones drove away with her children, Paul, 3, and Edie, 18 months, strapped in the back seat, she said.

It was about 8:30 p.m. on July 15, and Jones allegedly had been on the run from police for a half-hour, initially in a stolen Infiniti, which authorities said he abandoned before taking Plaia's Mercedes. All told, the pursuit, which began in Baltimore and ended in Anne Arundel County, lasted two hours, crossing six Maryland jurisdictions at speeds of up to 130 mph and causing officials to briefly close the Chesapeake Bay Bridge.

Jones is facing numerous criminal charges. In Montgomery, he is on trial on charges of carjacking, assault and two counts of kidnapping children. If convicted, he could be sentenced to 100 years in prison, authorities said.

Jones "forced [Plaia] to live out her worst nightmare," Assistant State's Attorney Deborah Armstrong told jurors in her opening statement yesterday, adding, "We will ask you to conclude the final chapter of this ordeal."

Jones's attorney, Rene Sandler, told the jury, "This is not a case of kidnapping."

"At the end of the case, you and your conscience will have to decide whether Mr. Jones in fact took this vehicle," Sandler said in her opening statement. "At the end of this case, I am confident the state will not prove . . . that my client is guilty of kidnapping."

Plaia said that when she encountered Jones that night, she was driving home to Great Falls with her children after visiting relatives in Potomac.

Authorities said Jones, at the wheel of a stolen Infiniti Q45 and being tracked by a police helicopter, drove south at high speeds from Baltimore on Interstate 95, took the Capital Beltway to Montgomery County, then jumped out of the car as it was rolling to a stop, its gas tank empty. A Baltimore officer, Bill Shiflett, testified that he watched from the helicopter as Jones tried to flag down motorists on River Road.

One vehicle sped past, Shiflett said.

The second vehicle was Plaia's.

Shiflett testified that as the helicopter descended to an altitude of about 100 feet, he watched the assailant pull Plaia from the car. She tried to open one of the back doors to reach her children, but the SUV pulled away.

The Mercedes got on the Beltway, then on I-95, speeding north to the Baltimore Beltway. Along the way, it swerved around other vehicles and sometimes traveled on the left shoulder of the roads. At Liberty Road and Interstate 695 in Baltimore County, police set up a roadblock. The Mercedes made a U-turn and headed south on I-695.

It was the second failed roadblock of the night. The first had been in Baltimore, shortly after the Infiniti was reported stolen. Police said Jones evaded four more roadblocks before finally being stopped in the eastbound lanes of Route 50 near the border of Anne Arundel and Prince George's counties. A police officer cut off the Mercedes, and Jones allegedly rammed the police car. Police said Jones then ran away but was caught after a brief foot chase.

Paul Plaia was still in his safety seat, with a scratch and bruise on his face, his mother testified. Paul's baby sister was unharmed.

Marna Plaia's voice quavered yesterday as she recalled watching her SUV pull away.

"My daughter was whimpering a little, and my son looked at me," she said, tears welling her eyes. "He just looked terrified."

Defendant Carl E. Jones listens as Marna Plaia testifies. Police say Jones led them on a chase across six jurisdictions that caused the Chesapeake Bay Bridge to be closed.