“On August 27 [2002], an NSA [National Security Agency] listening post intercepted a satellite telephone call placed from somewhere in Karachi, Pakistan, to a known al Qaeda operative. …On September 9 [2002]…Pakistani security forces bagged three Yemenis after an extended exchange of gunfire. One of them was Ramzi bin al-Shibh, who was well known to U.S. intelligence as one of the key al Qaeda planners of the September 11 attack. The call that NSA had monitored coming out of Karachi two weeks earlier had come from his phone. Subsequently, additional al Qaeda phones and laptops were found in Pakistan and eventually turned over to NSA. The telephone numbers and e-mail addresses in the memories of the phones and laptops were downloaded and fed into NSA’s burgeoning databases of numbers and addresses of known or suspected al Qaeda members, which were under full-time monitoring. Those telephone numbers or e-mail addresses that were located in the United States were passed to the FBI for investigation.”
– Matthew M. Aid, The Secret Sentry, Page 233