The investigation into the fatal collision involving a FedEx truck and a college tour bus continued Sunday.

Eyewitnesses to the scene claim that the truck appeared to be on fire before it crashed into the college tour bus. Despite what witnesses to the crash have said, officials stated that at present there’s no evidence the FedEx truck was burning before it hit the bus.

National Transportation Safety Board member Mark Rosekind said in a statement that there is simply no physical evidence available to support the claim. Rosekind did not rule out the possibility of a pre-impact fire; it’s simply impossible to prove at this point and time.

The statement may signal just how devastating this vehicular collision truly was.

Authorities had already informed the press that they expected it would be some time before they were able to determine the cause of the deadly crash. Much of the difficulty is blamed on the extensive damage caused by the fire.

BREAKING: NTSB: Crash scene yields no evidence that truck was on fire before deadly California bus crash.

— The Associated Press (@AP) April 13, 2014

Investigators struggle to confirm details of California crash as inquiry opens http://t.co/9ehhmAZhEL

— The Guardian (@guardian) April 13, 2014

The tragic collision occurred on Thursday. High school students were being transported upstate to Humboldt State University. The teenagers were to embark on a tour of the campus and then perhaps take the necessary steps to become students at the university.

A FedEx tractor-trailer traveling south on I-5 plowed across the green median divider and crashed directly into the bus. Soon after there was a fiery explosion that engulfed both vehicles in flames.

Though dozens of passengers were able to escape the bus with their lives, 10 people did not survive. Among the deceased are five high school students and three adult chaperones. Both drivers were killed.

The crash occurred 100 miles north of Sacramento, Calif. and is said to have been heard for miles.

Investigators have already determined that the FedEx truck collided into the bus without having ever braked.

Though the ongoing investigation has not found evidence of the pre-collision fire, some believe that it could signal that a mechanical failure was at the root of the tragic accident.

Image via YouTube