The fact of the matter is that as from the moment you announce a bomb threat or a hijack to the authorities then you are no longer really the captain of your aircraft.
It may help to know that command of the aircraft passes to the senior policeman present on parking.
Would the two posters who have made such definitive statements - not so much as a "I think" or a "it may be the case" etc. to be found in either - please be good enough to cite the grounds for such emphatic statements?
The fact that so many pilots - presumably the majority of posters here at least think they are pilots - are willing to entertain the notion that they loose their responsibilities and authority in such circumstances is very telling indeed. For starters, it seems to provide excellent grounds for taking that authority away. Actually, when you think about it, why should a captain who declares a low fuel state be allowed to be in charge of the aircraft? Would it not be better to hand the matter over to ATC? Actually, when you think about it, do we really need pilots at all?