Because the anthrax came from a state: the sophistication of the weaponization process tells you that. If the anthrax came from the state, then the ultimate sponsor of 9-11 was a state. States can't run and hide, unlike terrorists. Any state sponsor of an act on the scale of 9-11 could not hope to survive, without some serious back-end security built in to the plan. The anthrax is the back-end security.
I don't follow you here. How does the Anthrax provide back-end security for the state that sponsored the 9-11 attack?