He had with him, in his arsenal (fner fner) the 'Good Book'.
Basically, God told him to do it. Which is alright then. Yeah.
I presume he was discreet about his motiviations and intentions to have survived this far:
Yank Loon said:
Hi mister, ahm from de United States of America good buddy, yo, and the good lord has sent me on a mission of the highest importance to the people of our freedom-loving country. Ahm here to kill, sir, yes, kill, with my sword of righteous justice, the man I have come to call bah many names, Bielzabub, Satan, the Devil and others, but you may know him as 'Osama Bin Laden'. Ah can see from the black, dusty towel around yo head that you are too a man of the cloth, so perhaps you could direct me to him, and then y'all have a good day sir.
Whoever the guy is, it is pretty safe to say he fits the bill of what this website calls "ally". Having the motivation to do this thing and have the nuts to carry it off to the extent that he was damned near the place where the so-called shaykh is holed up when he was caught is pretty impressive to say the least.
And there are no prizes in thinking it will make a reasonably good Hollywood B-movie into the bargain.