If I had all the answers to this question I would write a book. I have a plausible theory of how 911 could have been pulled off, but since all of the physical evidence has been eliminated and the rest hidden behind the National security cloak by the administration there is very little to talk about beside just speculation. If your really interested you should investigate where Cheney was and what he was doing the morning of 911. What happened to Tower 7 and why did it have to collapse? Did a plane really hit the Pentagon? Was Mohammed Atta CIA?
Like a mystery? Here is a important clue, what deduction can you make from this?