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Former President George W. Bush and first lady Laura Bush pause after laying a wreath in the reflecting pool at ground zero on Sept. 10, 2006, a day before the fifth anniversary of the 9/11 attacks, in New York.
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Former President George W. Bush and first lady Laura Bush pause after laying a wreath in the reflecting pool at ground zero on Sept. 10, 2006, a day before the fifth anniversary of the 9/11 attacks, in New York.
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President Barack Obama shakes hands with a New York Police Department officer after a wreath laying ceremony at the National Sept. 11 Memorial at ground zero in New York, on May 5, 2011. The visit marked the death of al Qaeda leader Osama bin Laden, who was killed by American forces in Pakistan on May 1.
AP Photo/Charles Dharapak
President Barack Obama observes a moment of silence during a wreath laying ceremony at the National Sept. 11 Memorial at ground zero in New York, on May 5, 2011. The visit marked the death of al Qaeda leader Osama bin Laden, who was killed by American forces in Pakistan on May 1.
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Venezuelan President Hugo Chavez, center, tours the site of the World Trade Center on Nov. 10, 2011, in New York.
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Pope Benedict XVI prays during his visit to ground zero in New York, on April 20, 2008.
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Pope Benedict XVI prays during his visit to ground zero in New York, on April 20, 2008.
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Sarah Palin, then-governor of Alaska, touches a relief plaque memorializing the victims of the 9/11 attack at the Tribute WTC Visitor Center next to ground zero, on Sept. 25, 2008, in New York.
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Prince Albert II of Monaco listens to Richard Sheirer, director of the Office of Emergency Management, while touring the World Trade Center site in New York, on Oct. 23, 2011.
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Queen Elizabeth II pauses after laying a wreath at the site of the World Trade Center on July 6, 2010, in New York.
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Queen Elizabeth II and Prince Philip, the Duke of Edinburgh, pause after laying a wreath at the site of the World Trade Center on July 6, 2010, in New York.
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Britain's Prince Harry pauses after laying a wreath at the site of the World Trade Center site on May 29, 2009, in New York.
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Gloria Macapagal Arroyo, then-president of the Philippines, tours ground zero on Nov. 16, 2011, in New York.
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Prince Alwaleed Bin Talal Bin Abdulaziz of Saudi Arabia tours ground zero with Laurence Levy, former deputy counsel of New York City mayor's office, on Oct. 11, 2011, a month after the 9/11 World Trade Center attacks, in New York.
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Sen. John McCain, then-Republican presidential nominee, hugs a construction worker at the reflecting pool at ground zero on the seventh anniversary of the 9/11 terrorist attacks, on Sept. 11, 2008, in New York.
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Former New York Governor David Paterson, Vice President Joe Biden, his wife Dr. Jill Biden, New York Mayor Mike Bloomberg and New Jersey Governor Chris Christie drop flowers into a reflecting pool in the middle of ground zero in New York, on Sept. 11, 2010, the anniversary of the terrorist attacks.
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Former Spanish Prime Minister Jose Maraia Aznar, right, and his wife, Ana Botella, left, tour ground zero with then-New York Mayor Rudolph Giuliani on Nov. 30, 2001, in New York.
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Former Chilean President Ricardo Lagos, left and former Argentinian President Fernando de la Rua tour ground zero on Nov. 10, 2011, in New York.
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Crown Prince Haakon and Crown Princess Mette-Marit of Norway tour ground zero on Oct. 29, 2010, in New York.
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Ugandan President Yoweri Kaguta Museveni tours the site of the World Trade Center on Nov. 11, 2011, in New York.
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Irish President Mary McAleese pauses during a wreath laying ceremony near a memorial wall at the site of the World Trade Center on March 14, 2002, in New York.
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Former New Jersey Governor Jon Corzine pauses during a 9/11 memorial ceremony at ground zero on Sept. 11, 2009, in New York.
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Former Uruguayan President Jorge Batlle tours ground zero with Omar Alvarellos, right, assistant to then-New York City Mayor Rudy Giuliani, on Nov. 10, 2011, in New York.
AP Photo/Mark Lennihan
Prince Phillippe and Princess Mathilde of Belgium look at plans of the World Trade Center with Bill Baroni, second from left, deputy executive director of the Port Authority of New York and New Jersey, during their visit to ground zero, on June 23, 2011, in New York. Joe Daniels, far left, is the President and CEO of the National September 11 Memorial and Museum.