The head-on collision of two trains in Los Angeles that killed at least 24 people and injured 135 others was probably caused by the passenger train's failure to stop at a red signal, according to rail company officials.
"At this moment we must acknowledge that it was a Metrolink engineer that made the error that caused yesterday's accident," Denise Tyrrell, a spokeswoman for the passenger train line, said at a news conference.
She said the engineer worked for a subcontractor used by the Metrolink rail company. It was not immediately known whether the engineer was killed or injured.
Several coaches were derailed and a fire broke out when the passenger train and a freight train collided, in Chatsworth, north of Los Angeles.
The death toll is expected to rise as emergency workers continue to search the wreckage. Of the 135 people injured, 45 were in critical condition.
Dozens of rescue workers rushed to the scene in an effort to free passengers from the wreckage. Much of the passenger train was badly twisted.
Both trains were traveling at about 65 km/h according to Metrolink.
There were 222 people on the Metrolink train, and three Union Pacific employees aboard the freight train, according to media reports.
Workers were searching for the event recorders carried by the two trains and the dispatch station recording involving the crash were to be turned over to investigators on Saturday.
The event recorders, like the so-called black boxes carried by airliners, monitor the actions of engineers on the trains and should provide investigators with crucial information regarding the cause of the collision.