In pictures: The U.S. commemorates the 25th anniversary of 9/11

A visitor pauses at one of the reflecting pools at the National September 11 Memorial & Museum at ground zero on the 25th anniversary of the Sept. 11 terror attacks.Jeenah Moon | Getty ImagesOn Sept. 11, 2001, members of al-Qaida hijacked four passenger airliners. They flew two planes into the twin skyscrapers of the World Trade Center in New York at 8:46 a.m. and 9:03 a.m., and both towers collapsed that morning. A third plane crashed into the Pentagon in Arlington County, Virginia, while a fourth — believed to have been headed for the U.S. Capitol — crashed into a field in Shanksville, Pennsylvania, after passengers attempted to retake control of the plane.The coordinated attacks became the deadliest terrorist attack on U.S. soil, killing 2,977 people in New York, at the Pentagon and aboard the four hijacked planes, excluding the 19 hijackers. The attacks led directly to the U.S.-led invasion of Afghanistan and helped usher in a broader U.S. "war on terror" that also included the 2003 invasion of Iraq.On the attack's 25th anniversary, Americans are remembering the victims with moments of silence and ceremonies at Ground Zero, the Pentagon and in Shanksville. Former Presidents...