Possible eye-witness and or camera evidence of any mid-air event (Explosion)which may have occurred within the aircraft..???
Apparently they were flying in very close formation (according to witness in BBC report). If there was a bomb on board, doesn't sound too clever...
I'm also intrigued to know why the military do this. I can't think of any plausible circumstance (except total comms and nav failure) that it is helpful - we generally have better navigation equipment, and better all-weather capability than they do. All they do is alarm passengers (and me!).
If they do need to intercept in order to take the extreme measure of shooting us down in case of hijack, then I'd prefer they kept out of sight!