Re: Assertions about laws, morals, and ethics as concerns the US response:
US law allows for action to be taken against OBL, as does the UN Charter. The US just has to claim to be acting in self-defence.
I suspect, however that OBL and his type see US Law as morally bankrupt and irrelevant.
Personally I've got no problem with hunting down anyone who supports the eradication of every Jew in Palestine, or those who seek to support or justify it.