Bin Laden stopped publicly denying responsibility at least as early as 2004. You're free to disbelieve that but don't ignore it in your haste to convince others. You might find that it has the opposite effect from the one you intend.

And as I looked at those demolished towers in Lebanon, it entered my mind that we should punish the oppressor in kind and that we should destroy towers in America in order that they taste some of what we tasted and so that they be deterred from killing our women and children.

http://english.aljazeera.net/archive/2004/11/200849163336457...