Actually, contemporaneous news reports said AMI employees recalled that the first anthrax letter arrived about the 8th of September 2001. The man who was the first fatality (from AMI in South Florida) began feeling sick around the last week of September — or about two weeks after 9/11.
In addition, there is solid, if circumstantial evidence that connects Atta and his gang to AMI and possibly the anthrax. They rented an apartment from the real-estate-agent wife of the head of AMI. They took flight lessons in the same vicinity as AMI. Atta and one of the other hijackers sought medical help for symptoms that appeared to be chemical burns. One sought treatment for a black lesion on his leg. The doctor who treated him believed the lesion was caused by an anthrax infection.
There is no question that someone continued the mailings after Atta and his known gang died in 9/11 attacks. But it is not unreasonable, given the known evidence, that Atta's gang began the mailings in South Florida just days before the hijackings. It would mean that there is at least one unknown member of Atta's gang who finished the mailings and who, in all likelihood, is still alive; possibly even still in the U.S.