Duh, this is all happening a few minutes drive from the 9/11 hijackers' main nest. We know the hijackers wanted a method of delivering either chemical or biological weapons, because they tried to get their hands on crop-dusters. Unless this turns out to be some kind of freak coincidence -- which I don't think is going to happen -- then it's as plain as the nose on your face who did it.
If a third party were involved, they could be involved in the original WTC incident.
Who says OBL and his group are the ONLY ones involved. Perhaps a silent partner "sweetened" the pot for them by throwing in some bio-terrorism???
Duh, or no Duh, you still haven't named the "obvious" contributor of the Anthrax. Remember that the Chinese have contributed other technologies to the Taliban.