Ceremonies mark 17th anniversary of 9/11 attacks (42 images)

Ceremonies mark the 17th anniversary of the terrorist attacks on September 11, 2001, in which four airliners were hijacked. Two crashed into the World Trade Center in New York City, another hit the Pentagon in Washington, D.C. A fourth, headed for D.C., crashed in Shanksville, Pa. Nearly 3,000 people were killed.

A flower is seen on a bench at the National 9/11 Pentagon Memorial. Photo by Kevin Dietsch/UPI

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Vice President Mike Pence, his wife Karen Pence, Defense Secretary James Mattis (R) and Vice Chairman of the Joint Chiefs of Staff Air Force Gen. Paul J. Selva, lay a wreath the the National 9/11 Pentagon Memorial. Photo by Kevin Dietsch/UPI

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Family members arrive for the 17th anniversary memorial service for the 9/11 terrorist attacks, at the National 9/11 Pentagon Memorial. Photo by Kevin Dietsch/UPI

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Flower are seen on a bench at the National 9/11 Pentagon Memorial. Photo by Kevin Dietsch/UPI

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