LOS ANGELES — The Metrolink spokeswoman who announced that a deadly train crash was caused by an engineer's mistake resigned Monday because the railroad's board had called her words "premature," even though they were later backed up by investigators.

The Friday afternoon crash between a Metrolink commuter train and a freight engine left at least 25 people dead. On Saturday, railroad spokeswoman Denise Tyrrell made a swift announcement blaming the engineer driving the Metrolink train for failing to stop at a red light and causing the head-on crash.

Tyrrell says she has quit because a Metrolink board statement called her announcement "premature."

The National Transportation Safety Board confirmed on Sunday that the engineer, who was killed in the crash, had failed to stop at the final red signal.

Investigators had no definitive answer as to why the commuter train carrying 220 people rolled past stop signals Friday and barreled head-on into a Union Pacific train in Chatsworth. The accident, the nation's deadliest rail disaster in 15 years, left train cars so mangled that some bodies had to be removed in pieces.

As commuters were returning to the trains Monday for the first workday since the crash, officials hoped to have the entire line ready by the end of the day. ."Our staff is looking to do what we can to help the families of the passengers affected by this tragedy," Metrolink spokesman Steve Lantz said. "We hope never to have this happen again. We hope people will have their confidence returned to ride with us."

National Transportation Safety Board member Kitty Higgins said Sunday night that audio recordings from the commuter train indicate a period of silence as it passed the last two signals before the fiery wreck, a time when the engineer and the conductor should have been peforming verbal safety checks.

She cautioned, however, that the train may have entered a dead zone where the recording was interrupted.

Higgins said the NTSB would measure the distance between the signals along the track on Monday. Investigators also want to interview the conductor, who was injured, about the recording, she said.

"He'll be able to tell us whether he recalls the engineer calling out and him confirming those signals," Higgins said.

NTSB Investigators also determined Sunday that the train failed to stop at the final red signal, which forced the train onto a track where the Union Pacific freight was traveling in the opposite direction, Higgins said at a news conference. The announcement confirmed Tyrrell's earlier statements.

Higgins said the commuter train was traveling 42 mph at the time of the crash.

NTSB experts are also planning to review the cell phone records of two 14-year-old boys and the engineer, who died in the crash, after the teens had told CBS2-TV that they received a text message from 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.

Data show that the Metrolink train ran the red light signal with devastating consequences.

"The Metrolink train went through the signal, did not observe the red signal and essentially forced open this section of the switch," Higgins said. "The switch bars were bent like a banana. It should be perfectly straight."

Higgins said experts still must examine whether the signal was working properly and were in the Metrolink engineer's line of sight.

However, she stressed that obeying signals on the track was an engineer's responsibility at the helm of a train.

"My understanding is it is very unusual for an experienced engineer to run a red light," she said.

Metrolink said earlier Sunday that a dispatcher tried to warn the engineer of the commuter train that he was about to collide with a freight train but the call came too late. The dispatcher reached the conductor in the rear of the train, but by then it had already crashed into the oncoming Union Pacific train, Metrolink officials said.

However, the NTSB contradicted Metrolink's report. Higgins said that the dispatcher noticed something was wrong, but before he could contact the train, the conductor — who survived — called in to report the wreck.

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.

The commuter train was heading from Union Station in downtown Los Angeles to Ventura County. 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, Michael Blood, Daisy Nguyen, Christina Hoag, Greg Risling, Justin Pritchard, James Beltran, John Rogers, Shaya Tayefe Mohajer and Gillian Flaccus contributed to this report.