WILLOWS, Glenn County (CBS SF) — The California Highway Patrol said Friday it could take months before investigators determine what caused the fiery crash between a student tour bus and a FedEx tractor-trailer on Interstate 5 in Glenn County that killed 11 people, including 6 students.

The CHP and Glenn County officials held a news briefing Friday morning, with speakers offering condolences to the families of those killed in Thursday evening’s crash involving the student bus headed to tour Humboldt State University.

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Both the driver of the FedEx truck and the tour bus were killed in the crash in the town of Orland, about 150 miles northeast of San Francisco. Three adult chaperones were killed in addition to the six students.

Hospital officials said 11 passengers were injured, including two in critical condition. Four others were listed in stable condition, while the  and five others were treated and then released.

Investigators do not yet have an idea why the FedEx driver crossed the median and slammed head-on into the bus, CHP Lt. Scott Frederick said.

“Since these are such in-depth, detailed investigations, we don’t expect to have a final report for a minimum of three months, 90 days,” Fredrick said. “It could take as long as six months depending on what the investigation entails.”

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The students on the bus were from  Southern California high schools.

The Glenn County Sheriff/Coroner Larry Jones said the last victim was removed from the crash site near Orland Friday morning. The intense fire from the crash meant and that it would take time to positively identify some of the victims, using dental records and in some cases DNA, said Jones.

Most of the victims were at the front of the bus, said Jones.

California State University Chancellor Timothy White said the “soul of CSU was cut deeply’ by the tragedy.

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The National Transportation Safety Board was set to open its own investigation. “Every piece of paper associated with this will be looked at,” said Eric M. Weiss, an NTSB spokesman.