20th anniversary of 9/11 attacks marked with ceremonies (35 images)

The 20th anniversary of the September 11, 2001, terror attacks was marked with ceremonies at the attack sites in New York City, Washington, D.C., and Shanksville, Pa., on Saturday.

Paul Murdoch, architect of the Flight 93 National Memorial, attends a ceremony marking the 20th anniversary of the 9/11 terrorist attacks at the Flight 93 National Memorial on Saturday. Photo by Archie Carpenter/UPI

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President Joe Biden along with Gordon Felt, president of the Friends of Flight 93, walks to the boulder that marks the sight of the crash of Flight 93 on Saturday. Photo by Archie Carpenter/UPI

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The Bells of Remembrance ring as the names of the passengers and crew lost in the crash of Flight 93 are read at the Flight 93 National Memorial on Saturday. Photo by Archie Carpenter/UPI

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The Bells of Remembrance ring as the names of the passengers and crew lost in the crash of Flight 93 are read at the Flight 93 National Memorial on Saturday. Photo by Archie Carpenter/UPI

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