As im about to head out, read this article:
http://www.counterpunch.org/cockburn11012004.html
This should help you.
That doesn't really seem to address the issue of how getting hold of Bin Laden, or bringing him to trial, would help to prevent the 9/11 attacks from occurring, unless he had some reason to say something about future attacks. But the US didn't want him to find out about stuff in the future, they wanted him to put on trial for the Cole attacks, primarily. Similarly, we don't want OBL now to prevent future attacks, we want to put him on trial for his role in 9/11... and the USS Cole attacks... and possibly his role in the 1993 WTC bombing.
I mean, it's not like Jack Bauer is going to force him to tell us about the plan 2 hours before it happens. When the US looks for terror suspects, they're mostly looking for people after the fact to put on trial.
In fact, terrorism is such a threat precisely because it is so disorganized. This is what made the IRA such a pain in the ass for the British. Even if they'd taken down the head of the IRA at any given time, it wouldn't stop the cells from carrying out their individual missions. They didn't even have enough central contact for the leader to really harm them much if caught.
The Al Qaeda group appears to be organized along similar lines, albeit with a slightly different focus. Capturing or killing OBL well in advance of 9/11 would certainly have hurt funding and organization somewhat, but I don't know if we can really argue that that action alone would destroy their ability to conduct operations, especially so close to the 9/11 attacks.
