A timeline and photos of the Sept. 11 attacks on the U.S. 20 years ago
An American flag at ground zero on the evening of Sept. 11, 2001 after the September 11 terrorist attacks on the World Trade Center in New York City.(AP Photo/Mark Lennihan) An American flag at ground zero on the evening of Sept. 11, 2001 after the September 11 terrorist attacks on the World Trade Center in New York City.(AP Photo/Mark Lennihan)
