FBI Director Robert S. Mueller III (left) listens as Pima County Sheriff Clarence Dupnik speaks on Sunday in Tucson, Ariz. Mr. Mueller was on hand to oversee the investigation of the shooting of Rep. Gabrielle Giffords, who was shot in the head a day earlier during a speech at a local supermarket. (Associated Press)

FBI Director Robert S. Mueller III (left) listens as Pima County Sheriff Clarence Dupnik speaks on Sunday in Tucson, Ariz. Mr. Mueller was on hand to oversee the investigation of the shooting of Rep. Gabrielle Giffords, who was shot in the head a day earlier during a speech at a local supermarket. (Associated Press)