Vice President Joseph R. Biden Jr. (right), Defense Secretary Leon E. Panetta (center) and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, participate in a ceremony on Sunday, Sept. 11, 2011, at the Pentagon to honor victims of the Sept. 11 attacks. (AP Photo/Charles Dharapak)

Photo by: Charles Dharapak

Vice President Joseph R. Biden Jr. (right), Defense Secretary Leon E. Panetta (center) and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, participate in a ceremony on Sunday, Sept. 11, 2011, at the Pentagon to honor victims of the Sept. 11 attacks. (AP Photo/Charles Dharapak)