Good point. I'm not anywhere near ready to put the tinfoil hat on and say China was behind this.
I will say I'm very concerned that we're making the same mistake with China that we did the Arabs. Ignoring their presence and placing a low priority on intelligence assets to a potential threat.
As far as infiltration of our society goes, the Chinese make the Arabs look like pikers.
I will say that I do believe China knew about this attack and made sure their comrades were out of harm's way. We do know that other attacks were planned but didn't happen on 9-11.