Why were U.S. intelligence agencies criticized after the September 11 attacks?

Following the September 11, 2001, terrorist attacks, U.S. intelligence agencies—specifically the Central Intelligence Agency (CIA) and the Federal Bureau of Investigation—faced significant criticism for systemic failures in preventing the tragedy.1

The 9/11 Commission identified several critical lapses:

• Failure of Imagination: The primary criticism was a collective failure to grasp the depth and nature of the threat posed by al-Qaeda.1
• Information Sharing: Agencies failed to share vital intelligence. For example, the CIA tracked two hijackers, Nawaf al-Hazmi and Khalid al-Mihdhar, but did not place them on a watch list or notify the FBI, allowing them to enter the U.S. undetected.2
• Operational Follow-through: The FBI was criticized for its handling of the Zacarias Moussaoui case, where headquarters determined there was insufficient probable cause to search his belongings, despite warnings from field agents about his suspicious flight training.2
• Human Intelligence: Critics noted a lack of adequate human intelligence collection, which is essential for understanding the intentions of international terrorists.3

These failures led to major reforms, including the creation of the National Counterterrorism Center and the office of the Director of National Intelligence to improve coordination.14