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.
Osama bin Laden
Meanwhile, on November 8, 1990, the FBI raided the New Jersey home of El Sayyid Nosair, an associate of al-Qaeda operative Ali Mohamed. They discovered copious evidence of terrorist plots, including plans to blow up New York City skyscrapers. This marked the earliest discovery of al-Qaeda terrorist plans outside of Muslim countries. Nosair was eventually convicted in connection to the 1993 World Trade Center bombing, and later admitted guilt for the murder of Rabbi Meir Kahane in New York City on November 5, 1990.