Flight Recorders & Bunker Busters
Bunker busting weapons are designed to remain intact after impacting the ground at high speed, penetrating several meters of soil, before finally exploding.
Flight recorders should be designed the same way - able to survive impact, heat, etc. And I think they should record video information as well as sound.
With that information we would have no doubt as to the identity of highjackers and others who create disruptions on aircraft and buses.