I think there's a big chance someone IS setting Bin Laden up. How on earth can people be 90% sure it was him? Of course he's done suspicious things in the past, but why would this be his attack? He denied, so he if he was behind this, he has no desire to sacrifice himself for the Islam. This is not to say he didn't do it (the US has thousands of people doing research, and if they come up with his name, of course he could have done it) but it's not smart to look only at Bin while there are so many other possibilities (One theory is that only the hijackers themselves planned this operation and that they're all dead now. So who'll be punished if ther's no clear evidence? That's right: Bin Laden)
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The last arrow of Legolas kindled in the air as it flew,
and plunged burning into the heart of a great wolf-chieftain.
All the others fled. -J.R.R. Tolkien, The Lord of the Rings
Legolas, mourning for the USA