WASHINGTON - Investigators looking into Monday's deadly D.C.-area transit-train crash focused yesterday on why a computerized anticollision system failed to halt the onrushing train, even though there is evidence that the operator tried to slow it down.

At the time of the crash, the Metro train that plowed into one stopped ahead of it was also operating in automatic mode, meaning it was controlled by computer.

In that mode, the operator's main job is to open and shut the doors and respond in case of an emergency.

Debbie Hersman, an investigator with the National Transportation Safety Board, said it was unclear if the emergency brake was actually engaged when the crash occurred. But the mushroom-shaped button that activates it was found pushed down in the operator's compartment.

Hersman said it was not clear when the button was pressed or how it got that way. She also said there was evidence of braking on the train's rotors, indicating it was likely the operator tried to slow down.

The crash occurred at the height of the evening rush hour, killing nine people and injuring more than 70 in the deadliest accident in the 30-year history of the Washington Metropolitan Area Transit Authority.

Crews spent yesterday pulling apart the wreckage and searching for victims while investigators tried to determine why the train's safeguards apparently did not kick in.

"That train was never supposed to get closer than 1,200 feet, period," said Jackie Jeter, president of a union of Metro workers.

Yesterday, all Metro trains were running on manual control as a precaution against computer malfunction.

The NTSB also focused on why the train cars fared so poorly, their attention drawn to the age of the cars in the moving train, which were among the fleet's oldest, dating to the system's founding.

The crash occurred on the red line near the District of Columbia-Maryland border, in an area where higher train speeds are common because there are longer distances between stops. Trains can go 55 to 59 m.p.h., though it was not clear how fast the train that crashed was traveling.

This isn't the first time that Metro's automated system has been called into question.

In June 2005, Metro experienced a close call in a tunnel under the Potomac River. A train operator noticed he was getting too close to the train ahead of him even though the system indicated the track was clear. He hit the emergency brake in time, as did the operator of a train behind him.

Metro attributed the problem in that incident to a defective communications cable.

Also, the signal relays that control trains were replaced after a serious safety warning in May 2000 by the Federal Railroad Administration. The warning came after failed relays were detected on the system.

The operator of the train that barreled into the stopped cars Monday was identified by Metro officials as Jeanice McMillan, 42, of Springfield, Va.

Investigators want McMillan's cell-phone and texting records to determine whether she was distracted before the crash, Hersman said.

Ayesha Thomas, a Metro employee who worked with McMillan, said McMillan would often work the late shift. She did not have a car and if she was unable to get a ride home, she would sleep at Metro's offices, take the first train to Franconia, Va., and return to work later that day.

"There is no evidence whatsoever that this driver has done anything to cause this accident," Metro general manager John Catoe said.

The transit network is supported by the District of Columbia, Maryland, and Virginia jurisdictions it serves. However, it has no dedicated funding source and has long pleaded for more funding, including from the federal government.