Robert Peraza, who lost his son Robert David Peraza, pauses at his son's name at the North Pool of the 9/11 Memorial at the site of the World Trade Center. Justin Lane/pool/Getty Images hide caption

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Singer Patti LaBelle performs during the "Concert For Hope" event, hosted by Washington National Cathedral, to mark the tenth anniversary of the 9/11 terrorist attacks. Alex Wong/Getty Images hide caption

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Alan Jackson

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Keri McMorrow, 7, visits the memorial pool where her uncle's name is engraved, during tenth anniversary ceremonies of the September 11, 2001 terrorist attacks at the World Trade Center site. Pool/Getty Images hide caption

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Kids and Sept. 11: The Day 'Children Realized ... Grownups Were Vulnerable'

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Paul Simon singing 'The Sound of Silence'

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President Obama looked out at the North Pool of the 9/11 Memorial in New York earlier this morning. Andrew Burton/Getty Images hide caption

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Cellist Yo-Yo Ma at the Sept. 11 service in New York

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The "Tribute in Light" illuminates the sky in New York on the 10th anniversary of the Sept. 11 attacks. Timothy A. Clary/AFP/Getty Images hide caption

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Special Coverage: Hour One

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