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A Moment of Silence - President Barack Obama laid a wreath at Ground Zero Thursday, paying tribute to victims of the Sept. 11, 2001, terrorist attack in New York. During his trip to New  York, the commander in chief also met with families of 9/11 victims and first responders.  (Photo: AP Photo/Charles Dharapak)

Photo By AP Photo/Charles Dharapak

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Carrying the Wreath - President Barack Obama prepares to lay the wreath.(Photo: AP Photo/Charles Dharapak)

Photo By Photo: AP Photo/Charles Dharapak

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Giving Thanks\r - The president and former New York City Mayor Rudy Giuliani meet with firefighters and first responders.\r(Photo: AP Photo/Charles Dharapak)

Photo By Photo: AP Photo/Charles Dharapak

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A Momemtous Visit - President Obama meets with firefighters and first responders at Engine 54, Ladder 4, Battalion 9 before visiting the National Sept. 11 Memorial at Ground Zero.(Photo: AP Photo/Charles Dharapak)

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Photo Op\r - The president shares a light moment with New York's Bravest. \r(Photo: AP Photo/Charles Dharapak)

Photo By Photo: AP Photo/Charles Dharapak

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The Wall of Honor - The president finishes viewing a bronze memorial plaque for the 15 men the firehouse lost as a result of the terror attack.(Photo: AP Photo/Charles Dharapak)

Photo By Photo: AP Photo/Charles Dharapak

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Rebuilding the Site\r - Ground Zero is seen from the north side of the site.\r(Photo: AP Photo/Seth Wenig)

Photo By Photo: AP Photo/Seth Wenig

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Standing Guard - The day before the president's visit, heavily armed officers stand guard at Ground Zero.(Photo: AP Photo/Mary Altaffer)

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On Alert - New York City police officers stand guard outside Ground Zero.(Photo: AP Photo/Mary Altaffer)

Photo By Photo: AP Photo/Mary Altaffer

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Sept. 11, 2001 - The twin towers of the World Trade Center burn behind the Empire State Building in New York. (Photo: AP Photo/Marty Lederhandler, File)