Newsweek investigates whether the CIA and FBI ignored critical clues that might have helped prevent the attacks. The first story looks at a case where the CIA tracked two suspected terrorists to an Al-Qaeda summit in Malaysia in 2000. These same two men later came to the U.S., lived in California and went on to hijack the plane that crashed into the Pentagon on Sept. 11. The report questions why the CIA didn't do more to stop these men, based on the information they had. The second story reports although one FBI informant was the hijackers' roommate, intelligence agencies still failed to recognize the threat. The third story reveals how an Saudi student in the U.S., Omar Al-Bayoumi, provided critical assistance to the two hijackers. The fourth story reports on how Saudi-based Islamic charities have been used to fund terrorist organizations around the world.