The thing is that even the people who claim that 9/11 is handiwork of Osama have failed miserably in providing concrete proof of ALQ's direct involvement, why do people expect to see "concrete proof" for these charges?
What proof do you require?
Khalid Sheikh Muahmmed, OBL, Zawahiri and the rest have openly acknowledged they plotted and carried out 9/11.
Why are you in this denial mode. I would expect this kind of conspiracy nonsense form Hanibal or marasi_dee but not you Captain1