Yeah, I must say I'm still thinking of the extreme Muslims... But, in the end does it matter? Al-Quida (no, I don't care about how its spelt), took credit for it, and even if they didn't do it, that doesn't stop them from being dicks.
Although, there is always the possibility that the aliens teamed up with the anchient eqyptians/ monkeys/ space ninjas/ normal ninjas, dragging all of the greatest elements of earths timeline into one moment, to cause a HUGE CATACLYSMIC EVENT!!!!!!
Wait... it was just two buildings falling over....
nvm.