Just a few more obvious questions to be asked of the defence: like for instance, who signed for the aircraft, exactly, i.e. who was officially in command? The tug driver? (or should it be tug pilot?)
If the pilots were not operating the aircraft, who started the engines?
Does the connection of the tug disable the aircraft brakes? (Surely, the crew must still have just a teensy-weensy bit of direct control remaining?)
Perhaps the crew should have remembered the last ditch line of defence - if you must drink and drive/fly, don't breathe.