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 United States' 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.
In addition, CBS Station KCAL correspondent Kristine Lazar reported exclusively that one minute before the crash, a teenager received a text message on his cell phone from the engineer, whom friends identified as Robert Sanchez.
The text message received told where Sanchez would be meeting another passenger train.
But train enthusiasts who knew Sanchez well doubt that he was to blame. They called their friend professional and caring. To a man, they said he would "never" have been reckless or unprofessional.
Another of Sanchez's friends, teenager Evan Morrison, told Lazar that Sanchez "was not the kind of guy who would run a red light."
When asked by KCAL to comment on the report, Metrolink spokesperson Denise Tyrell said, "I can't believe someone could be texting while driving 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. "
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.
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, 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, Alabama, moments after the trestle was damaged by a towboat; 47 people were killed.