I'd like to add to John Blakely's comments, reproduced by Brian Dixon, above.
The 'logic' used by the Air Marshals appears to be that if ZD576 didn't deviate its track from the point at which the waypoint was changed until impact, then it must have been guided to its impact point under full control of the pilots. However, this is a false supposition. I suggest that the fact that the aircraft didn't turn towards its new waypoint may well indicate that it was no longer under the full control of the pilots, whether due to control jam, UFCM, FADEC-induced engine runaway or whatever. It may seem an alien concept to some, but it is perfectly possible to fly in a (broadly) straight line, whilst being 'out of control'.
Further, their airships' suggestion that the pilots were already negligent by the time of the waypoint change, because they were flying too quickly, is also absurd if, as seems likely, they were flying in the clear air that seems to have been present beneath the 800-900 ft overcast.