President Barack Obama greets 14-year old Payton Wall at the site of the National September 11th Memorial and Museum at Ground Zero in New York, N.Y., May 5, 2011. The President received a letter from Wall, who lost her father in the World Trade Center attack, and asked that she be invited to the ceremony. Standing with Wall are her mother Diane, her sister Avery, and friend Madison Robertson, who also lost her father on 9/11. (Official White House Photo by Pete Souza)