"For well over a decade international terrorism has been a major concern of the U.S. Intelligence Community. Collection assets of all kinds have long been focused on Al Qaeda and other terrorist groups. Intensive analytical expertise has been devoted to determining such groups memberships, locations, and plans. Intelligence agencies had been acutely aware of the danger for years. In February 2001, Director of Central Intelligence (DCI) George Tenet publicly testified to Congress that 'the threat from terrorism is real, it is immediate, and it is evolving.' Furthermore, '[Osama] bin Ladin and his global network of lieutenants and associates remain the most immediate and serious threat.' Nevertheless, the Intelligence Community gave no specific warning of the September 11, 2001 attacks. Although all observers grant that terrorist groups are very difficult targets and that undetected movements of small numbers of their members in an open society cannot realistically be prevented, serious questions remain. An extensive investigation by the two intelligence committees of the September 11 attacks was announced on February 14, 2002. Whatever the findings of the investigation, the roles and missions of intelligence agencies, their organizational relationships, and their operational capabilities will be reviewed to enhance capabilities against terrorism."
CRS Report for Congress, RL31292
United States Department of State: http://fpc.state.gov/