Los Angeles ? A commuter train engineer who ran a stop signal was blamed Saturday for the nation’s deadliest rail disaster in 15 years, a wreck that killed 25 people and left such a mass of smoldering, twisted metal that it took nearly a day to recover all the bodies.

A preliminary investigation found that “it was a Metrolink engineer that failed to stop at a red signal and that was the probable cause” of Friday’s collision with a freight train in Los Angeles’ San Fernando Valley, Metrolink spokeswoman Denise Tyrrell said. She said she believes the engineer, whose name was not released, is dead.

“When two trains are in the same place at the same time somebody’s made a terrible mistake,” said Tyrrell, who was shaking and near tears as she spoke with reporters.

Authorities later announced that the effort to recover bodies from the Metrolink train’s crushed front car had ended, with the death toll at 24. It rose to 25 when USC Medical Center spokeswoman Adelaide DeLaCerda said a 50-year-old man transported to the hospital from the wreck died Saturday. She would not release his name.

“It was a very, very difficult operation,” Mayor Antonio Villaraigosa said. “It was like peeling an onion to find all the victims there.”

A total of 135 people were injured, with 81 transported to hospitals in serious or critical condition. There was no overall condition update available Saturday, but a telephone survey of five hospitals found nine of 34 patients still critical. Many were described as having crush injuries.

Firefighter Searcy Jackson III, a 20-year veteran and one of the first to pull bodies from the wreckage, said he had never seen such devastation. The 50-year-old said his team pulled one living passenger from the train and cut the mangled metal to remove about a half-dozen bodies.

“The metal was pushed together like an accordion,” Jackson said.

Firefighters who extricated the dead from the wreck were rotated in and out of the scene to prevent emotional exhaustion, fire Capt. Armando Hogan said.

“There are some things we are trained for, there are some things I don’t care what kind of training you have, you don’t always prepare for,” Hogan said. “This situation, particularly early on, with people inside the train, with the injuries, and with people moaning and crying and screaming, it was a traumatic experience.”

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.

“Even if the train is on the main track, it must go through a series of signals and each one of the signals must be obeyed,” Tyrrell said. “What we believe happened, barring any new information from the NTSB, is we believe that our engineer failed to stop … and that was the cause of the accident.”