WILLOWS, Calif. -- Investigators on Friday sifted through the wreckage of the fiery Northern California crash that killed 10 people, including five high school students, and said they did not yet know what caused the driver of a FedEx truck to veer across a freeway median and hit the students' bus head-on.
California Highway Patrol Lt. Scott Fredrick said it remained unclear whether the FedEx driver – who officials said was among those killed – had fallen asleep, whether his freight truck had some type of mechanical failure or if it was involved in separate collision that preceded the fiery crash.
Fredrick said CHP investigators were being assisted by the National Transportation Safety Board, which sent a team that arrived about 10 a.m. Friday. Investigators would use "sophisticated surveying and mapping equipment," along with 3-D diagramming, to reconstruct what led up to the crash, he said.
Fredrick said investigators would also consider roadway and weather conditions at the time. But he and others cautioned it could take up to six months for the CHP to complete its report.
"The investigation itself … is a long, tedious process," said Ruben Leal of the CHP. "We may not have some answers for months."
The first call about the crash came in about 5:40 p.m. Thursday, said CHP Cmdr. Bruce Carpenter. The bus was "already fully engulfed in flames" by the time first responders arrived, he said.
Carpenter said 31 people were transported to seven hospitals with injuries ranging from minor to critical. Nine people were pronounced dead at the scene, and another died later of severe burns.
The final body was removed from the scene early Friday morning, officials said.
Officials said a sedan was also involved in the crash, but did not elaborate how. Two occupants were treated for injuries described as minor to moderate, Leal said, but were expected to be OK.
Because of the extent of the injuries to those killed, Glenn County Sheriff-Coroner Larry Jones said it was "much more difficult" to positively identify them. He said medical and dental records would be used, and toxicology reports conducted on the drivers involved.
More than a dozen agencies responded to the crash, which Jones said was heard up to a quarter-mile away. "This was a horrific collision," he said.
Officials with the Los Angeles Unified School District – which had 19 students on board – along with Humboldt State University and the California State University system, were also at the news conference to lend their condolences. "The great irony here, the great sadness, is these are the students California needs to be successful going forward," CSU Chancellor Timothy White said, saying the students "had their dream of going to Humboldt State taken away by this tragic accident."
"The soul of the CSU has been cut deeply," he said.
Meanwhile, one surviving passenger said the bus was running late and had been involved in a minor collision earlier in the trip.
Calvin Aceves, 17, told the Sacramento Bee in a videotaped interview that he and two students from San Diego were picked up by the bus and that the driver was running late. He said the minor crash slowed them down another 30 minutes.
Upon reaching Sacramento, Aceves said another driver took over as the bus continued toward Humboldt State. After falling asleep, Aceves said he awoke to the sound of screams and the squeal of brakes, and then felt the impact of the crash.
"I just heard the screaming, and I was halfway asleep so I thought I was dreaming," said Aceves, who was seated in the middle seats. "I turned my head a little and I see fire. Just a ball of fire."
Aceves said he began banging on a window of the bus in a panic, as students pushed and shoved each other in the aisles.
"People were in shock," he said. "It seemed that people did not know how to react."
Once outside, he said students ran to the shoulder of the road.
"Everyone was in shock."
Early Friday, a FedEx spokeswoman confirmed that a company "freight truck" was involved in the collision. In a statement, FedEx said, "We are cooperating fully with the authorities as they investigate."
In a statement, Silverado Stages officials said they were "helping the authorities in gathering information regarding the tragic accident that occurred on Thursday evening. Our top priority is making sure that the injured are being cared for. Our thoughts and prayers are with the injured, their families and everyone affected by this accident." Humboldt State officials said the charter bus was bringing a group of prospective students to the campus' April 12 spring preview day.
University officials made use of the school's website to report what they knew. An emergency information line for the Humboldt State University police was made available to family members seeking their loved ones, at (707) 826-6327.