I'm reminded that Mohammed Atta and Marwan al-Shehhi checked out the flight school in Norman, and that Zacarias Moussaoui trained there. Now, of all the flight schools in America, why pick one in Norman, Oklahoma? One answer would be that the hijackers had friends and contacts - a sleeper cell - in Norman.
Two guys that assisted Moussaoui from Norman ended up in jail. One most of us knew from around town. Creepy guy with a beard so long he tied it -- used to seem him around campus and downtown -- haven't seen him since he was arrested after 9-11 and hope that holds.