Kitty Higgins, a board member for the National Transportation Safety Board, says her agency is also talking with the two teens and their families. The teens told KCBS-TV that they received a text message from the engineer at 4:22 p.m. Friday, just moments before the deadly crash.
Higgins says that the engineer's cell phone was not recovered at the crash site Sunday.
She declined to say what the teens and their families have told investigators thus far.
The engineer died in the wreck.
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A dispatcher tried to warn the engineer of a Metrolink commuter train that he was about to collide with a freight train but the call came too late, rail officials investigating the crash that killed 25 people said Sunday.
The dispatcher reached the conductor in the rear of the train, but by then it had already crashed into the oncoming Union Pacific engine at 40 mph, Metrolink officials said.
The engineer was killed in the accident, the nation's deadliest rail disaster in 15 years.
Metrolink said the engineer ran a red signal, but federal investigators said it could be a year before they determine a cause.
The National Transportation Safety Board said Sunday it was looking into a report that the engineer may have been text messaging around the time of the crash.
Two days after the crash, men wearing green and orange safety vests walked up and down the tracks Sunday in an early morning fog, while others snapped pictures and climbed inside the wrecked shell of the front passenger car.
A teenager told CBS2-TV that he had exchanged a brief text message with the engineer shortly before the crash. The Los Angeles station said the teen was among a group of youths who befriended the engineer and asked him questions about his work. The station showed an interview of the teen holding a cell phone with a text message apparently signed by the engineer and dated 4:22 p.m. Friday, shortly before the crash.
Metrolink spokeswoman Denise Tyrrell said before the report aired that she would find it "unbelievable" that an engineer would be text messaging while operating a train.
NTSB spokesman Terry Williams said he couldn't confirm reports that the engineer, whose name was not released, had been text messaging.
"We're going to look into that, anything that can help us find the cause of this accident," he said.
Earlier, NTSB member Kitty Higgins said similar reports in other accident investigations turned out to be inaccurate "so I want to be very, very careful about it."
Some 135 were injured in the crash.
Dr. Marc Eckstein, medical director for the Los Angeles Fire Department, said survivors' injuries included partially severed limbs and legs flayed to the bone. At least two survivors had to be extricated from underneath dead bodies and six victims were discovered under the train Saturday, he said.
"There were bodies cut in half, and I could see torsos sticking out. It was pretty horrific," Eckstein said. "The bodies were entwined with the wreckage."
Eckstein said all rescue personnel were required to check in with a staff psychologist before leaving the scene - but many, including himself, preferred to deal privately with what they saw. "All you can do is go home and hug your wife and kids, I guess," he said. "These people were regular working people like you and I and headed home looking forward to a weekend with their families - and they're dead in an instant."
Keith Millhouse, vice chairman of the Southern California Regional Rail Authority's board of directors and a Moorpark city councilman, said he plans to take the train Monday in an effort to restore the public's trust in Metrolink.
"It's unfair to say it's an unsafe operation," Millhouse said. Rescue crews recovered two data recorders Saturday from the Metrolink train and one data recorder and one video recorder from the freight train. The video has pictures from forward-looking cameras and the data recorders have information on speed, braking patterns and whether the horn was used.
Families of victims struggled with their loss after the coroner's office released a partial list of the names of the dead. Among them was a Los Angeles police officer and a city employee who was believed to work in the general services office, said Mayor Antonio Villaraigosa.
Spree Desha, 35, had worked for the Police Department for seven years and spent much of her career training new officers. She had been honored 34 times for performance and professional qualities. "She sat in the first train (car) as a matter of practice, in uniform, so if someone came on the train and made trouble, she was ready to help out," Assistant Chief Jim McDonnell said. "That was just the way she did business."
Larry Remata, 58, said he was in Hawaii visiting his 100-year-old mother and rushed home when he got news that his wife, Donna, was among the dead.
"Right now, I am grieving. It is starting to hit me a little bit. Especially seeing her name in the newspaper - it hurt me more," he said.
There were no new reports of fatalities from hospitals Sunday, and the scene was cleared of bodies, said Lt. Cheryl MacWillie of the county coroner's office.
The collision occurred on a horseshoe-shaped section of track in Chatsworth at the west end of the San Fernando Valley, near a 500-foot-long tunnel underneath Stoney Point Park. There is a siding at one end of the tunnel where one train can wait for another to pass, Tyrrell said.
At a news conference late Saturday, the NTSB's Higgins said it was too early to determine what caused the crash but noted that a pair of switches that control whether a train goes onto the siding were open. One of them should have been closed, Higgins said. "The indication is that it was forced open," possibly by the Metrolink train, Higgins said.
The commuter train, heading from Union Station in downtown Los Angeles to Ventura County, was carrying 220 passengers, one engineer and one conductor when it collided with the Union Pacific freight, which had a crew of three. The impact rammed the Metrolink engine backward, jamming it deep into the first passenger car.
It was the deadliest passenger train crash since Sept. 22, 1993, when Amtrak's Sunset Limited plunged off a trestle into a bayou near Mobile, Ala., moments after the trestle was damaged by a towboat; 47 people were killed.
Associated Press writers Thomas Watkins, Amy Taxin, Daisy Nguyen, Christina Hoag, Greg Risling, Justin Pritchard, James Beltran, John Rogers and Gillian Flaccus contributed to this report.