A photo taken on September 11, 2001 by the New York City Police Department as the North Tower collapses, engulfing lower Manhattan in smoke and ash.

(Photo: AP Photo/NYPD, Det. Greg Semendinger)

For ... more 
A photo taken on September 11, 2001 by the New York City Police Department as the North Tower collapses, engulfing lower Manhattan in smoke and ash.

(Photo: AP Photo/NYPD, Det. Greg Semendinger)

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Fri, Sep 9, 2011 7:29 PM EDT