Memorial Museum

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A view of the National September 11 Memorial Museum with the north reflecting pool in foreground during the museum's dedication ceremony in New York on Thursday, May 15, 2014. (AP Photo/Justin Lane, Pool)

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President Barack Obama and first lady Michelle Obama, along with former Secretary of State Hillary Rodham Clinton and former President Bill Clinton tour the Memorial Hall at the National September 11 Memorial Museum with former New York Mayor Michael Bloomberg, Thursday, May 15, 2014, in New York. (AP Photo/Carolyn Kaster)

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Members of the general public watch a screen projection on the World Trade Center Plaza during the dedication ceremony at the National September 11 Memorial Museum in New York on Thursday, May 15, 2014. (AP Photo/ Anthony Behar, Pool)

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President Barack Obama speaks at the dedication ceremony for the National September 11 Memorial Museum on Thursday, May 15, 2014 in New York. (AP Photo/Mike Segar, Pool)

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People try to look through the windows of the National September 11 Memorial Museum during the museum's dedication in New York, on Thursday, May 15, 2014. (AP Photo/Justin Lane, Pool)

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President Barack Obama, first lady Michelle Obama, former New York City Mayor Michael Bloomberg, former Secretary of State Hillary Rodham Clinton, former President Bill Clinton, and Diana Taylor, tour the Memorial Hall at the National September 11 Memorial Museum, Thursday, May 15, 2014, in New York. (AP Photo/Carolyn Kaster)