Authorities also said Juan Manuel Alvarez told them he had poured gasoline on the SUV before the Metrolink struck it Jan. 26 as it carried commuters to downtown Los Angeles.
Police initially believed Alvarez had meant to remain in the truck but then lost his nerve and fled. He and his wife, Carmelita Alvarez, had separated, and she had obtained a restraining order against him, police said.
Police Chief Randy Adams said Alvarez may have considered suicide, but "the investigation has revealed that his actions are not consistent with that of an individual who is attempting to follow through with that act."
"His actions were deliberate with the intent of causing a horrific tragedy," Adams told reporters Thursday.
Alvarez, 25, pleaded not guilty Tuesday to 11 counts of murder and an arson charge. Prosecutors have not decided whether to seek the death penalty.
Defense attorney Eric Chase said the police statements were "not only vicious and callous but are a reckless distortion of the facts."
"If they want to make this case about, as they say, Juan Alvarez's intent to cause a horrific tragedy, I hope they can back it up. Apparently the Glendale police have not seen enough blood and are hungry for more," Chase said in a statement.
Authorities, who had previously released few details about the arson charge, said Thursday that witnesses reported seeing a man park next to the tracks and douse a vehicle with liquid. Sgt. Tom Lorenz, a police spokesman, said Alvarez described pouring gasoline on and inside the vehicle.
Police said they asked Alvarez what he thought would happen if a vehicle were left in the path of an oncoming train.
"He basically stated that he thought there would be an explosion," said Lt. Jon Perkins, the case's lead detective.
Alvarez was ordered jailed without bail pending a March 16 hearing to determine whether there is enough evidence to try him.