I studied aircraft accident investigation in college. Fun fact, you can tell if a fire occurred on post crash or in mid air by analyzing which metals have melted and cross referencing their melting points to fire temperatures. Fires burn much hotter in air because the constant flow of oxygen.

Another fun fact. In prop airplanes you can tell if the engines were running at high speed vs if they running on low power based off the way the props are bent. If they are bent forwards then they were running at high speed at the time of impact and if they are bent backwards towards the aircraft then they were running at low speed.