(former firefighter) I would look to local and state police for their reports. Any fatal accident with a possibility of foul play, or obvious foul play (DUI, etc) resulted in us assisting the State Police reconstruction team while they processed the scene, measuring and photographing everything to the millimeter, because once we cleaned it up, there was no going back.

That said, I've also seen plenty of crazy vehicle accidents, including fires, many of which are hard to explain how they could have happened. For example, a car where the entire drivers side was smashed into the back seat from driving into a telephone pole. The driver's survival story? "Thank god i wasn't wearing a seatbelt and my car had a bench seat"... She moved over at the last second.

Seatbelts don't always save lives...