July 31, 2001 - The FAA issues another warning to airlines advising that "terror groups are known to be planning and training for hijackings."
Aug. 6, 2001 - Bush receives a CIA report about al-Qaida and the possibility of airline hijackings. The warning is passed on to embassies and other overseas facilities.
Aug. 15, 2001 - The Pan Am International Flight Academy in Minnesota alerts the FBI to their suspicions about Zacarias Moussaoui. He had paid for the training in cash and requested instruction on flying large jets, even though he had little experience.
Aug. 16, 2001 - The FAA issues an alert about "disguised weapons." Airlines are alerted the terrorists might use common objects such as cell phones or clothespins as weapons.
Aug. 17, 2001 - Zacarias Moussaoui is arrested on charges of overstaying his 90-day visa. The FBI interrogates Moussaoui for two days before he requests a lawyer.
Aug. 23, 2001 - CIA director George Tenet, concerned that an al-Qaida attack is imminent, orders the CIA to search their files for leads. An urgent cable is sent to the FBI, State Department, Customs and INS, alerting them to the CIA's concerns about Nawaf Alhazmi and Khalid Almihdhar. After the INS reports that Almihdhar re-entered the country on July 4, the FBI begins searching for them.
Sept. 4, 2001 - The national security advisers to President George W. Bush approve a draft version of a plan to combat al-Qaida. It includes provisions for $200 million to arm the enemies of the Taliban. The advisers plan to present the draft to Bush on Sept. 10, however the president is traveling and does not see it.
Sept. 10, 2001 - The National Security Agency intercepts two communications from Afghanistan to Saudi Arabia. One says, "Tomorrow is zero hour," and the other says "The match begins tomorrow." The messages are not translated until Sept. 12.