Investigators Tuesday scoured the wreckage of two commuter trains hunting for clues to the worst subway accident in Washington's history which killed nine people and injured some 80 others.
Metro officials said they still had no clue why one train plowed into the back of another on an above-ground section of the system's Red Line just at the start of Monday's evening rush hour.
But the National Transportation Safety Board (NTSB), the federal agency that has taken over investigation of the crash, said the striking train was among the oldest in Metro's 33-year history, and that its operator had been driving the system's subway trains for just three months.
The driver, Jeanice McMillan, 42, whose train slammed into the other one with such force that it thrust two carriages from the front one up onto her train, died in the crash.
Preliminary investigations determined that the striking train was in "automatic mode" and that the emergency brake had been depressed, indicating the operator may have tried to stop the train, the NTSB's Debbie Hersman said.
"We have not yet made any determination about the cause of this accident," she told a press conference near the scene of the crash.
"We haven't ruled anything out," Hersman added, acknowledging that the NTSB had formally requested access to McMillan's mobile phone records but stressed that that was "not a specific area we are singling out."
Last September, 25 people were killed when the conductor of a commuter train in Los Angeles was sending text messages on his mobile phone while at the controls.
NTSB had 19 investigators proceeding with a painstaking probe of Monday's accident which turned a routine commute into a nightmarish disaster scene.
They would soon gain access to nine recorders on the newer, struck train -- data Hersman expected would shed light on what may have caused train 112 to plow into train 214 which was stopped on the same track.
Hersman said maintenance had been performed earlier in June on the "train control system" at the area where the crash occurred.
Concerns have focused on the computerized signal system designed to prevent train collisions, and on the age of train 112, one of Metro's 1000-series trains delivered from 1975 to 1978.
"We are aggressively seeking to replace the 1000-series railcars... and we had taken action before this tragedy to achieve that objective," Washington Metropolitan Area Transit Authority (WMATA) board chairman Jim Graham said.
Hersman said it was too early to say whether train 112's age or McMillan's relative lack of experience were determining factors in the crash.
"Our first thoughts and first efforts here in DC are with the families and friends of the victims," Washington Mayor Adrian Fenty said Tuesday in the aftermath of the collision he described as "harrowing."
Fenty said the final death toll stood at nine, with eight of the dead identified, including David Wherley, who had led the Washington chapter of the National Guard, and his wife Ann Wherley.
"I had the opportunity to work with him as he commanded the troops in DC and as he sent them off to war," said a visibly moved Fenty as he noted how he personally made phone calls to some of the victims' relatives.
"You can not imagine the shock, the pain, the horror and the disbelief of the family members who are survivors,"
Metro said the cause of the crash remained a mystery, and that the investigation could take several weeks or months.
"We are committed to investigating this accident until we determine why this happened and what must be done to ensure it never happens again," Metro General Manager John Catoe said in a statement.
As in many mass-transit systems, on-board computers control Metro trains' speed and braking, while another system monitors to see if there is a safe distance between trains, and automatically apply brakes if they get too close.
The collision involving the two six-compartment trains took place at 5:02 pm (2102 GMT) near the Fort Totten Metro station, on the northern edges of Washington near the neighboring state of Maryland.
Thousands of government employees ride the Metro into work each day in a five-line rail system that carries about 800,000 people daily from the suburbs in the states of Maryland and Virginia.
The only other Metro crash involving passenger fatalities was in January 1982, when three people died after a derailment.
