District of Columbia Police Chief Cathy Lanier briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. Standing to the right of Lanier is District of Columbia Mayor Vincent Gray. At least one 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 Police Chief Cathy Lanier briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. Standing to the right of Lanier is District of Columbia Mayor Vincent Gray. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning (AP Photo/Susan Walsh)