There were 19 hijackers in the September 11 attacks, part of an Islamic terrorism group called Al-Qaeda. The 19 hijackers hijacked four aircraft; American Airlines Flight 11 had five hijackers and crashed into the North Tower of the World Trade Center, United Airlines Flight 175 had five hijackers and crashed into the South Tower of the World Trade Center, American Airlines Flight 77 had five hijackers and crashed into the Pentagon, and United Airlines Flight 93 had four hijackers and crashed outside of Shanksville, Pennsylvania.