President Obama hugs Diane Wall, wife of Glen James Wall who died at the World Trade Center attack, after laying a wreath at the National Sept. 11 Memorial at ground zero in New York Charles Dharapak / AP Photo President Barack Obama observes a moment of silence after placing a wreath at the World Trade Center site. Richard Drew / AP Photos President Obama lays a wreath at the 9/11 Memorial in New York on May 5, 2011. Jewel Samad / AFP/ Getty Images President Obama arrives with staff where he will lay a wreath at ground zero on May 5, 2011. Timothy A. Clary / AFP / Getty Images A view of construction at the World Trade Center site on May 5, 2011 in New York City. Spencer Platt/Getty Images President Obama meets with police officers and first responders at the First Precinct before visiting the National Sept. 11 Memorial at ground zero in New York, May 5, 2011. Charles Dharapak / AP President Obama addresses firefighters at the Midtown Firehouse (Engine 54, Ladder 4, Battalion 9) in New York on May 5, 2011 after arriving in New York to participate in a wreath laying ceremony at the 9/11 Memorial. Jewel Samad / AFP/ Getty Images President Obama views a memorial honoring deceased members of the New York City Fire Department at the Engine 54 firehouse on May 5, 2011 in New York City. ohn Angelillo-Pool / Getty Images President Obama steps off Air Force One at JFK Airport in New York, May 5, 2011, en route to ground zero. Charles Dharapak / AP Photos Vice President Biden lays a wreath during a ceremony to honor the victims of the September 11, 2001 terrorist attack at the Pentagon, on May 5, 2011. Mark Wilson / Getty Images New York City police officers stand guard outside ground zero ahead of President Obama's visit, May 5, 2011. Mary Altaffer / AP Photos A U.S. soldier walks by newspaper clippings on a wall at ground zero heralding the death of Osama bin Laden on May 2, 2011. Spencer Platt / Getty Images