World Trade Center

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People gather during a ceremony marking the 10th anniversary of the attacks on the World Trade Center Sunday, Sept. 11, 2011, outside the World Trade Center site in New York. (AP Photo/Oded Balilty)

NewYork Firefighter Zachary Fletcher embraces his mother Monica Fletcher after finding his twin brother Andre G. Fletcher's name engraved at the south pool of the National September 11 Memorial during a ceremony marking the 10th anniversary of the attacks at World Trade Center, Sunday, Sept. 11, 2011 in New York. (AP Photo/Mary Altaffer)

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A flag rests on a panel inscribed with the names of those killed on 9/11 at the National September 11 Memorial at the World Trade Center site in New York, Sunday, Sept. 11, 2011. (AP Photo/Seth Wenig, Pool)

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A woman runs her hand over one of the names inscribed on the wall by the north pool of the Sept. 11 memorial, Sunday, Sept. 11, 2011 in New York, as the public gathered to commemorate the 10th anniversary of the terrorist attacks at the World Trade Center. (AP Photo/David Handschuh, Pool)

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People pause by the waterfall pool at the National September 11 Memorial before a planned ceremony marking the 10th anniversary of the attacks at the World Trade Center site, Sunday, Sept. 11, 2011, in New York. (AP Photo/Matt Rourke)

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A woman cries over a name on the edge of the south pool at the National September 11 Memorial in New York during the ceremony marking the 10th anniversary of the attacks on the World Trade Center in New York, Sunday, Sept. 11, 2011. (AP Photo/Timothy A. Clary, Pool)

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People gather during a ceremony marking the 10th anniversary of the attacks on the World Trade Center Sunday, Sept. 11, 2011, outside the World Trade Center site in New York. (AP Photo/Oded Balilty)

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The World Trade Center ceremony marking the 10th anniversary of the attacks, takes place at the National September 11 Memorial, Sunday, Sept. 11, 2011 in New York. (AP Photo/Mark Lennihan)

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People pay their respect during a ceremony marking the 10th anniversary of the attacks on the World Trade Center Sunday, Sept. 11, 2011, outside the World Trade Center site in New York. (AP Photo/(AP Photo/Oded Balilty)

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A New York City police officer salutes at the north pool of the Sept. 11 memorial as the national anthem is sung during the 10th anniversary ceremonies at the World Trade Center, Sunday, Sept. 11, 2011, in New York. (AP Photo/Justin Lane, Pool)

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Jacqueline Arana, of Union City, N.J., sheds a tear at 8:46 a.m., marking when the first plane hit the World Trade Center in 2001, during a ceremony in Lower Manhattan, Sunday, Sept. 11, 2011, marking the 10th anniversary of the attacks at the World Trade Center. (AP Photo/Craig Ruttle)

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President Barack Obama, foreground, runs his hand along the names on the Sept. 11 memorial as former President George W. Bush, Laura Bush and Michelle Obama look on during a visit to the memorial during the 10th anniversary ceremony at the site of the World Trade Center Sunday, Sept. 11, 2011, in New York. (APP Photo/Timothy A. Clary, Pool)

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President Barack Obama and former President George W. Bush greet family members of those who died during the attacks on the World Trade Center at the National September 11 Memorial during a ceremony marking the 10th anniversary of the attacks at World Trade Center, Sunday, Sept. 11, 2011 in New York. (AP Photo/Mary Altaffer)

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Former President George W. Bush, left, and former first lady Laura Bush, along with President Barack Obama, second from right, and first lady Michelle Obama along with others, marking the 10th anniversary of the Sept. 11 attacks, pay their respects at the National September 11 Memorial at the World Trade Center site in Sunday, Sept. 11, 2011, in New York. (AP Photo/Matt Rourke)

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Robert Peraza, who lost his son Robert David Peraza in the attacks at the World Trade Center, pauses at his son's name at the North Pool of the 9/11 Memorial before the 10th anniversary ceremony at the site, Sunday Sept. 11, 2011, in New York. (AP Photo/Justin Lane, Pool)

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A police officer's white-gloved hand touches names on the wall surrounding the north pool of the 9/11 Memorial during the tenth anniversary ceremony at the site of the World Trade Center, Sunday Sept. 11, 2011, in New York. (AP Photo/David Handschuh, Pool)

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Visitors hug near a memorial pool at the National September 11 Memorial at the World Trade Center site in New York, Sunday, Sept. 11, 2011. (AP Photo/Seth Wenig, Pool)

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Former first lady Laura Bush, from left, former President George W. Bush, first lady Michelle Obama and President Barack Obama hold hands to their hearts during the national anthem as friends and relatives of the victims of 9/11 gather for a ceremony marking the 10th anniversary of the attacks at the National September 11 Memorial at the World Trade Center site, Sunday, Sept. 11, 2011, in New York. (AP Photo/Jason DeCrow)

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Vasantha Velamuri, who's husband, Sankara Sastry Velamuri, was killed in the 9/11 terrorist attacks on the World Trade Center, mourns at the place where his name is inscribed on the Sept. 11 memorial at the World Trade Center site in New York during a ceremony to mark the 10th anniversary of the attacks Sunday, Sept. 11, 2011. (AP Photo/Carolyn Cole, Pool)

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The Tribute in Light shines above lower Manhattan, the Statue of Liberty, and One World Trade Center, left, Saturday, Sept. 10, 2011, in New York. Sunday will mark the 10th anniversary of the Sept. 11, 2001, attacks on the United States. (AP Photo/Mark Lennihan)