The investigation of a devastating California highway crash involving a FedEx tractor-trailer and college tour bus has revealed startling new details as to what happened.

On Thursday a FedEx truck traveling south on I-5 crossed a grassy median and collided with a college tour bus. Soon after there was a fiery explosion.

The fatal collision resulted in the deaths of ten people. Among the deceased were several teenagers and a Los Angeles couple that volunteered to be chaperones for the trip. The drivers of both vehicles were also killed.

In the aftermath of the tragedy, a federal investigation was launched in order to determine what led to the crash.

National Transportation Safety Board member Mark Rosekind said that when studying the scene of the crash it became clear that the truck left no tire marks on the road. This has led investigators to assume that the FedEx semi did not break before hitting the bus.

A couple that witnessed the accident told the Associated Press that before the truck jumped the median and eventually collided with the bus it appeared to already be on fire.

National Transportation Safety Board says no sign the FedEx truck braked before hitting bus in Northern California http://t.co/3zsWA6paa7

— NBC News (@NBCNews) April 13, 2014

Northern California bus crash: Black box recovered for bus, not FedEx truck http://t.co/wTxNTZyg9Y

— insidebayarea (@insidebayarea) April 13, 2014

Other witnesses thought they saw the truck clip a car ahead of crossing the median.

The fact that the semi appeared to already be on fire lends some credibility to the theory that the vehicle was suffering some form of mechanical failure prior to the crash. It could be that such a failure is the explanation for why the FedEx truck failed to break before hitting the bus.

There are various theories as to what led to the crash, including the possibility that the driver had fallen asleep at the wheel.

There are no definite explanations at the moment and investigators have already stated that it may be weeks before an actual cause is identified. Because both vehicles were utterly destroyed by fire, it’s going to be very difficult for officials to piece together what went wrong ahead of the crash.

“At this point all we can hope for is that they’re in a better place": Seven California bus crash victims identified http://t.co/qhdNWpG1Rc

— NBC News (@NBCNews) April 12, 2014

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