The University of Oklahoma was used as one of the staging areas for the 9/11 attacks. Zacarias Moussaoui took flight lessons in Norman, Oklahoma and was seen on the OU campus and using their facilities numerous times. Also, one of the Flight 93 hijacker's plane tickets was purchased online from an OU library internet terminal. Mohammed Atta was also a vistor to the Norman Al Qaeda cell.
indeed, the Oklahoma part of this is troubling. if AQ was going to conduct an operation and had choice of a target, something like the exiting crowd at fenway park would have gotten them alot more visibility.