District of Columbia Mayor Vincent Gray briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. A gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/Susan Walsh)

Photo by: Susan Walsh

District of Columbia Mayor Vincent Gray briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. A gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/Susan Walsh)