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.
Hijackers in the September 11 attacks
According to the 9/11 Commission Report, 26 al-Qaeda terrorist conspirators sought to enter the United States to carry out a suicide mission. In the end, the FBI reported that there were 19 hijackers in all: five on three of the flights, and four on the fourth. On September 14, three days after the attacks, the FBI announced the names of 19 persons. After a controversy about an earlier remark, U.S. Homeland Security Secretary Janet Napolitano stated in May 2009 that the 9/11 Commission found that none of the hijackers entered the United States through Canada.