Well, actually, your recall has merged elements of both sources. There is a pharmacist who was approached by one of the hijackers seeking medicine, a week or so prior to 9-11. There was also a doctor who was visited by another of the hijackers, and the doctor observed unusual symptoms that, once the anthrax attacks occurred, he realized were consistent with anthrax exposure.
A third hijacker went to an emergency room to get treatment for a lesion on his leg, ostensibly created by tripping over a piece of luggage. Anti-biotics were prescribed. Subsequently, the doctor concluded that the lesion was almost certainly cutaneous anthrax -- a diagnosis which did not occur to him at the time.