RED BLUFF, Calif. (AP) -- Federal investigators are looking into a driver's claim that a FedEx tractor-trailer was already on fire when it careened out-of-control across a freeway median and slammed into a bus taking high school students on a college tour, killing 10 people in a fiery wreck.
The investigators are looking for more witnesses who could corroborate the driver's claim, and planned to examine crash scene evidence for clues of a fire before the vehicles exploded into towering flames on a Northern California highway, National Transportation Safety Board member Mark Rosekind said Saturday.
He said the truck left no skid marks, on either the roadway or the median, as it veered into oncoming traffic, sideswiping a Nissan Altima before crashing into the bus. Five students, three adult chaperones and both drivers died in Thursday's collision on a stretch of Interstate 5 in Orland, a small city about 100 miles north of Sacramento.
Some of the victims were thrown from the bus, Rosekind said.
The woman who drove the sedan told investigators and a KNBC-TV reporter that flames were coming from the lower rear of the truck cab.
"It was in flames as it came through the median," Bonnie Duran said. "It wasn't like the whole thing was engulfed. It was coming up wrapping around him."
Initial reports by police made no mention of a fire before the crash.
The bus was gutted and the truck was a mangled mess after the fiery crash, making it difficult for investigators to determine whether a fire started in the truck before impact. Rosekind said investigators planned to look at blood tests to determine whether the FedEx driver inhaled smoke before the collision, and whether he was impaired.
A family member told the Sacramento Bee the truck driver was Tim Evans, 32, of Elk Grove, Calif.
A blood test will also be conducted for the bus driver, who had only been driving a short time after relieving another driver during a stop in Sacramento. Rosekind said more than 145 feet of tire marks showed that the bus driver tried to brake and swerve to the right to avoid being hit.
He said the bus' black box-style electronic control module was recovered and will be analyzed. The truck's device was destroyed, but other steps will be taken to analyze its speed and maneuvering.
In addition to the cause of the crash, federal transportation authorities are examining whether fire safety measures they previously recommended for motor coaches could have allowed more of the 48 bus occupants to escape unharmed.
Bodies recovered from the bus were charred beyond recognition. Dozens of students had injuries including burns, and several remained hospitalized.
Fire safety has been a longstanding concern of the NTSB.
After a 2005 bus fire killed 23 nursing home evacuees escaping Hurricane Rita in Texas, the agency called for safety standards that could make buses less vulnerable to fire, including improved protection of fuel tanks. More recently, the NTSB says buses must have sophisticated suppression systems to control fires, much as high-rise buildings have sprinkler systems.
The NTSB, which investigates accidents and their causes, has no authority to require safety changes it recommends.
But a bill passed by Congress in June 2012 directed the Department of Transportation to conduct research and tests on ways to prevent fires or mitigate the effects, among other safety issues. That included evacuating passengers, as well automatic fire suppression, smoke suppression and improved fire extinguishers. Representatives of the bus industry told Congress that manufacturers were increasingly and voluntarily adding such features.
As part of its investigation into Thursday's crash, the NTSB will also evaluate whether there should have been a barrier on the median to help prevent head-on collisions. Barriers are required when medians are less than 50 feet wide; this one was 60.
The 44 Southern California high school students on the bus, many hoping to become the first in their families to attend college, were on a free trip arranged by Humboldt State University. The university chartered two more buses to bring more than 500 prospective students to the campus for a three-day visit. Those who made it to the university were sent home earlier than scheduled Saturday morning in light of the tragedy.