By Olga Grigoryants
INDIO, Calif. (Reuters) - Investigators seeking the cause of a bus crash in California that killed 13 people, including the driver, examined wreckage on Monday for any data recorder to determine what might have led to one of the deadliest such U.S. collisions in the last decade, officials said.
Authorities said they still do not know how fast the bus, which was carrying casino patrons, was traveling when it rammed into the back of a tractor-trailer early on Sunday near Palm Springs, which is about 100 miles (160 km) east of Los Angeles.
"It's so early on that basically we can't say definitely what the cause of the accident was," California Highway Patrol (CHP) division chief Jim Abele told reporters.
Investigators have not found any data recorder on the bus and National Transportation Safety Board member Earl Weener said it was not clear if the 1996 model-year vehicle was equipped with one.
NTSB investigators will look into factors such as whether the bus driver was fatigued or under the influence of drugs or alcohol, as well as any mechanical factors, Weener said.
Thirty-one victims were taken to area hospitals, with the most badly hurt going to Desert Regional Medical Center in Palm Springs where, according to the facility, four remained in critical condition.
The tractor-trailer's driver, who was injured in the collision, has told investigators he was crawling along at 5 miles per hour (8 kmh), Abele said.
But CHP officials said that was not unusually slow because traffic was heavy at the time, as CHP officers had been slowing cars and trucks for a utility project.
It was clear the driver of the bus did not slam on the brakes before hitting the tractor-trailer, because there were no skid marks from the vehicle, Abele said.
The bus was ferrying casino-goers back to Los Angeles from the Red Earth Casino in Thermal, which is about 30 miles (48 km) southeast of Palm Springs, Abele said.
The Riverside County coroner's bureau on Monday identified most of the 13 people killed in the crash. They were listed as ranging in age from 52 to 72.
The driver was identified as Teodulo Vides, 59. He was the owner-operator of a charter company called USA Holiday, officials said.
(Writing by Alex Dobuzinskis; Editing by Leslie Adler, Bernard Orr)