Would it not be the equivalent of a what supremacist gang get into the army and get trained and do a couple tours here and there. Comeback home and all go to Canada and pull off a deadly attack? Should the US be blamed for training the group that messed up Canada? Or does the US get a pass because we are a hegemony?
Al-Quaeda was part of a network of Wahabist terror organisations; wahabism is chiefly sustained and funded by the Saudi establishment, and Al Quaeda had its financial base there. Most of the perpetrators of 9/11 were Saudi, and two of these had strong contact with Saudi intelligence. There are circumstantial pointers too, such as the head of Saudi intelligence being summarily dismissed days before the attacks, having served in post since 1979.