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Joe Biden, Leon Panetta, Mike Mullen

Chairman of the Joint Chiefs of Staff Adm. Mike Mullen, from left, Defense Secretary Leon Panetta, and Vice President Joe Biden stand during the playing of the National Anthem on the 10th anniversary of the September 11 attacks at the Pentagon in Washington, Sunday, Sept. 11, 2011. (AP Photo/Charles Dharapak)

9/11 Pentagon ceremony

Remembering the September 11, 2011 attack on the Pentagon.