Friday's fiery crash killed 25 people and injured 125 others, about 80 critically.
On Saturday Metrolink spokeswoman Denise Tyrrell said the crash was caused by an error from the engineer. Tyrrell said the engineer missed a signal light causing the Metrolink train to crash head on with an oncoming freight train.
However NTSB investigators will also be looking into whether the signal was working properly and whether the dispatchers warned the engineer of the imminent danger.
Investigators will also look at rumors that the trains engineer may have been text messaging in the moments leading up to the crash.
The engineer, who has not been officially identified, was among the people killed in the crash.
Investigators said they will seek cell phone records of two teenagers and the train engineer as they probe whether text messages factored into the crash.
The Los Angeles County Coroner's office released a partial list of people killed in the crash.
Families of three victims have not been notified and the coroner's office has not released their names.
The commuter train and a Union Pacific freight train collided in Chatsworth Friday afternoon, trapping passengers inside at least three Metrolink cars, one of which caught fire.
During the night, crews used hydraulic jacks to keep the passenger car from falling over and other specialized rescue equipment to gently tear apart the metal.
- Video: Train on fire
- Video: Train crash survivor describes what happened
- Video: Witness says 'It was bloody'
- Video: Men witness crash
- Video: Mayor Villaraigosa shocked
- Slideshow: Scene of accident
- Interactive map: Location in Chatsworth
The collision happened near Rinaldi Street, east of Topanga Canyon Boulevard and west of Canoga Avenue near Stoney Point Park, just south of the 118 Freeway near the Ventura County line. Firefighters set up a triage staging area at the park.
An LAPD officer was confirmed killed in the crash. Officer Spree Desha was an LAPD officer for seven years.
There were 250 firefighters on scene, said Barry. Civilians were among the firefighters and police that helped pull victims from the commuter train shortly after it crashed.
Los Angeles County Sheriff Lee Baca confirmed that the County Sheriff's Dept. was "effectively working for the city" during the rescue efforts.
Sheriff Baca said a uniformed deputy sheriff was onboard the train during the collision and sounded the alarm. That deputy reportedly suffered broken bones and a punctured lung.
According to Metrolink Spokesperson Denise Tyrrell, Metrolink train #111 originated out of Union Station in L.A. It was estimated that 350 passengers were on the train. Metrolink train #111 normally travels to Moorpark in Ventura County.
According to Union Pacific spokesperson Zoe Richmond, there are typically two crew members on each freight train voyage, the conductor and the engineer, both of whom occupy the lead locomotive engine. The spokesperson said the company had not yet been in contact with anyone from the stricken freight train.
The locomotive car of the Metrolink train pulled (not pushed) the rest of the commuter train. The collision was severe enough to push the locomotive car into the passenger car behind it. Three passenger cars were attached to the locomotive. The passenger cars do not have seatbelts for riders.
According to Tyrrell, Metrolink passenger cars weigh approximately 119 tons. The locomotive engines weigh approximately 450 tons.
Tyrrell said there was no word yet from the conductor of the Metrolink train. Conductors are sub-contractors and do not work directly for Metrolink.
The Union Pacific freight train had passed through a tunnel through the Santa Susana Pass that connects Simi Valley to Chatsworth. Metrolink Spokesperson Tyrrell said the tracks are used by Metrolink, Amtrak and freight trains.
Firefighters could be seen breaking windows to reach and rescue passengers inside one Metrolink passenger car.
A Sikorsky helicopter was at the scene Friday evening. The large helicopter is sometimes called a "floating hospital." An LAPD mobile sub-station arrived at approximately 6:40 p.m. Fire trucks were using Rinaldi St. as an access road to the crash.
Medics arrived quickly on scene after the crash. Several victims could be seen being treated at the scene by emergency personnel immediately after the crash.
At Stoney Point Park at the end of Heather Lee Lane, rescuers set up red, yellow and green and color-coded tarpaulins to distinguish the different injuries: Immediate (red), Delayed (yellow), and Minor (green). Helicopters were conducting airlifts from the parking lot of Stoney Point Park.
UCLA Medical Center has pointed out the need for blood donation at this time. People can donate blood to UCLA Medical Center between 8 a.m. and 1 p.m. Saturday. For more information on donating blood, go to the UCLA Blood and Platelet Center
In an unrelated accident, a Metrolink train collided with a car in Corona almost an hour after the Chatsworth crash. The driver of the car was killed and one passenger on that train was injured. The car was apparently attempting to cross the tracks. The crash happened on the 100 block of N. Sheridan St. in Corona, according to the Corona Fire Dept.