Donald Rumsfeld
The United States was attacked on September 11, 2001 by al Qaeda terrorists who hijacked commercial airliners and crashed them in coordinated strikes into both towers of the World Trade Center in Lower Manhattan, New York City and the Pentagon in Washington, D.C. The fourth plane crashed into a field in Shanksville, Pennsylvania, and its target was likely a prominent building in Washington, D.C., most probably either the Capitol Building or the White House. Within three hours of the start of the first hijacking and two hours after American Airlines Flight 11 struck the World Trade Center, Rumsfeld raised the defense condition signaling of the United States offensive readiness to DEFCON 3, the highest it had been since the Arab-Israeli war in 1973.
Responsibility for the September 11 attacks
Intelligence experts speak of a "short list" of prime suspects—groups that possess both the means and the motive to carry out the crime. Two of the passengers had been identified as al-Qaeda members and were on the FBI's terrorist-alert list prior to 9/11: Khalid Almihdhar and Nawaf Alhazmi. It appears certain that all hijackers had Arab origins, and none were Afghan; moreover, both in their immense scale, careful planning and refraining from claiming responsibility, the attacks are reminiscent of al-Qaeda's previous attacks such as the 1998 US embassy bombings that killed over 200 people.