Q: What was the most surprising revelation for you while you were researching and writing [The Looming Tower: Al-Qaeda and the Road to 9/11]?
A: [S]adly, [it] is that 9/11 could have been prevented if the CIA and the NSA had cooperated with the FBI by providing the information that two al-Qaeda hijackers had arrived in America in January 2000, nineteen months before the attacks. Personal rivalries and bureaucratic turf wars stood in the way. As a result, the hijackers remained in the country unobserved, and the attacks proceeded.
–Me, quoted in the Borzoi Reader Online (Alfred A. Knopf), August 2006