[aristeides]

The whole world may not have known. But apparently a whole lot of Moslems knew, including the head of the main mosque in Milan. And he at least -- and I assume virtually all the others who were in the know -- seem to have thought of it as a religious duty to keep the secret.

[Darlin']

Well, uh ... yes quite a lot of Moslems knew about it, after all they uh ... planned it.
Although lots of them knew something big was in the works and may have helped facilitate it in some manner, I expect no more than a handful knew exactly what, when, how. If they had something critical would have been leaked at some point but this was not a disorganized or hastily thrown together scheme. I agree that some of them participated because they felt it a religious duty especially some of the actual hijackers but I'd guess most of them, those on the sidelines, did so out of an inbred hatred.

[Dr. Eckleburg]

...to keep the secret.

But I thought the only people who believe it's possible for a large group to keep a big secret are "conspiracy theorists."

Or so I've been told.