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

itoggle caption Justin Lane/pool/Getty Images

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

itoggle caption Timothy A. Clary/AFP/Getty Images

Rick King, who was assistant fire chief of Shanksville, Pa., on Sept. 11, 2001, stands near a cross made from steel from the World Trade Center, outside the fire station in Shanksville on July 14. He was one of nine people to tell NPR what Sept. 10 was like, the day before the horrible events of Sept. 11. Gene J. Puskar/AP hide caption

itoggle caption Gene J. Puskar/AP

Outside the Pentagon, 184 benches are part of the memorial honoring those killed there on Sept. 11, 2001. Jose Luis Magana/AP hide caption

itoggle caption Jose Luis Magana/AP