NEW YORK - APRIl 3: (SEPTEMBER 11 RETROSPECTIVE) The 'Tribute in Light' memorial to the World Trade Center is seen from the Empire State Building April 3, 2002 in New York City.

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NEW YORK - SEPTEMBER 11: A New York City firefighters and Police stand at a reflecting pool at Ground Zero during the annual 9/11 memorial service September 11, 2010 in New York City. People gathered at the World Trade Center site to mark the ninth anniversary of the terrorist attacks that killed nearly 3,000 people on September 11, 2001.

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NEW YORK - OCTOBER 26: The construction site of the National September 11 Memorial & Museum is seen at ground zero October 26, 2010 in New York City. New York City Michael Bloomberg helped plant the 50th tree at the memorial site

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NEW YORK, NY - JUNE 30: The north pool waterfall is tested as work continues on the National September 11 Memorial & Museum at the World Trade Center site on June 30, 2011 in New York City. The memorial features two reflecting pools on the footprints of the twin towers. The memorial is scheduled to be dedicated on September 11, 2011, the tenth anniversary of the World Trade Center terrorist …

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NEW YORK, NY - JUNE 30: Work continues on the south pool at the National September 11 Memorial & Museum at the World Trade Center site on June 30, 2011 in New York City. The memorial features two reflecting pools on the footprints of the twin towers. The memorial is scheduled to be dedicated on September 11, 2011, the tenth anniversary of the World Trade Center terrorist attacks.

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NEW YORK, NY - JUNE 30: The north pool waterfall is tested as work continues on the National September 11 Memorial & Museum at the World Trade Center site on June 30, 2011 in New York City. The memorial features two reflecting pools on the footprints of the twin towers. The memorial is scheduled to be dedicated on September 11, 2011, the tenth anniversary of the World Trade Center terrorist …

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NEW YORK, NY - JULY 08: (This Image was made with a panoramic film camera and scanned into a digital file) The reflecting pools marking the footprints of the twin towers are seen as work continues at the National September 11 Memorial & Museum at the World Trade Center site on July 8, 2011 in New York City. More than 2,700 people were killed when al-Qaeda terrorists hijacked U.S. passenger jets …

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NEW YORK, NY - AUGUST 25: Construction continues on the National September 11 Memorial & Museum at the World Trade Center site on August 25, 2011 in New York City. The memorial features two reflecting pools on the footprints of the twin towers. The memorial is scheduled to be dedicated on September 11, 2011, the tenth anniversary of the World Trade Center terrorist attacks.(Photo by Mario …

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NEW YORK, NY - JULY 23: Work continues around the World Trade Center site as the World Trade Center cross was moved into its permanent home at the 9/11 Memorial Museum after a blessing ceremony on July 23, 2011 in New York City. The cross is an intersecting steel beam discovered in the World Trade Center rubble which served as symbol of spiritual recovery in the aftermath of 9/11.

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NEW YORK, NY - JULY 23: Construction workers lower the September 11 cross by crane into a subterranean section of the National September 11 Memorial and Museum on July 23, 2011 in New York City. The cross is an intersecting steel beam discovered in the World Trade Center rubble which served as symbol of spiritual recovery in the aftermath of 9/11

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NEW YORK, NY - AUGUST 22: An American flag hangs from a building at the World Trade Center site on August 22, 2011 in New York City. New York City and the nation are preparing for the 10th anniversary of the terrorist attacks on lower Manhattan which resulted in the deaths of 2,753 people in the attacks on the World Trade Center.

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NEW YORK, NY - AUGUST 25: Construction continues on One World trade Center (R) and the National September 11 Memorial & Museum (LOWER L) at the World Trade Center site on August 25, 2011 in New York City. The memorial features two reflecting pools on the footprints of the twin towers. The memorial is scheduled to be dedicated on September 11, 2011, the tenth anniversary of the World Trade Center …

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NEW YORK, NY - AUGUST 27: Mist shrouds the top of Freedom Tower, still under construction next to the September 11 Memorial and Museum and World Trade Center construction site, about 12 hours before Hurricane Irene is expected to arrive August 27, 2011 in New York City. The World Trade Center site is located inside the Zone A mandatory evacuation area but New York City Mayor Michael Bloomberg …

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NEW YORK - AUGUST 25: Construction cranes fill the air around Ground Zero in lower Manhattan as seen from the east August 25, 2010 in New York City. Work continues on the former World Trade Center site as activists have been lining up for and against a proposed Islamic cultural center and prayer room two blocks from the site.

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NEW YORK, NY - JANUARY 06: A view of Ground Zero is seen from the side of 1 World Trade Center January 6, 2011 in New York City. The tower has reached 52 floors, roughly halfway to its final height. Workers are adding nearly a floor a week to the building which will be the tallest in New York when it is completed in 2013.

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NEW YORK, NY - MAY 05: A view of construction at the World Trade Center site on May 5, 2011 in New York City. President Barack Obama is visiting Ground Zero today to participate in a wreath laying ceremony and to mark the death of Osama bin Laden.

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ARLINGTON, VA - JUNE 28: A quilt that features the victims of the Pentagon attack hangs on a wall of the Pentagon Memorial Quilts Corridor where 21 quilts, of more than 100 in the collection that serve as a historical record of the tragic events of 9/11, are on display June 28, 2011 in Arlington, Virginia. This year is the 10th anniversary of the September 11 terrorist attacks, in which 184 …

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ARLINGTON, VA - MAY 02: David Huber and Nicole Lozare of Arlington, Virginia, pay their respect to victims of the 9/11 terrorist attacks in the early morning of May 2, 2011, after President Barack Obama has announced the death of Osama Bin Laden, at the Pentagon Memorial outside the Department of Defense (Pentagon) in Arlington, Virginia. A special force led operation has killed Osama Bin Laden …

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ARLINGTON, VA - SEPTEMBER 11: (AFP OUT) A woman sits on a bench prior to an event to mark the anniversary of the 9/11 terrorist attacks at the Pentagon Memorial September 11, 2010 in Arlington, Virginia. U.S. President Obama will deliver remark and lay a wreath during the event on the 9th anniversary of the attack.

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NEW YORK, NY - JANUARY 06: A construction supervisor walks down a stairwell on the eastern face of 1 World Trade Center January 6, 2011 in New York City. The tower has reached 52 floors, roughly halfway to its final height. Workers are adding nearly a floor a week to the building which will be the tallest in New York when it is completed in 2013.

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NEW YORK - FEBRUARY 15: (SEPTEMBER 11 RETROSPECTIVE) As the sun sets over New Jersey, cleanup and recovery efforts continue at the site of the World Trade Center disaster February 15, 2002 in New York City.

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A mural honoring firefighters killed on 9/11 is seen outside the World Trade Center.

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WASHINGTON - OCTOBER 11, 2001: (SEPTEMBER 11 RETROSPECTIVE) U.S. President George W. Bush holds an American flag during a Memorial Service at the Pentagon October 11, 2001 in Arlington, Virginia.

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