Twelve killed in Washington Navy Yard Shooting

(AP) As many as three gunmen opened fire Monday inside one of the US Navy's oldest buildings, attacking office workers at a heavily guarded military facility in the heart of the nation's capital.



A police chief said as many as 12 were shot dead at Washington Navy Yard



One of the gunmen was dead, and police were searching for two other men believed to have joined in the attack at the Washington Navy Yard.



The suspects were reportedly dressed in military-style clothing, including one who had on a beret.



In all, more than a dozen people were shot, at least half of them fatally. It was not immediately clear whether that number included the dead gunman.



The attack unfolded just a short distance from the White House and the U.S.



Capitol at a former shipyard that is one of the Navy's oldest shore facilities.



The building that was targeted was the military's headquarters for Naval Sea Systems Command, which buys, builds and maintains ships, submarines and combat systems. About 3,000 people work at the headquarters, many of them civilians.



Witnesses described a gunman opening fire from a fourth-floor overlook, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway.



It was not clear whether the witnesses on different floors were describing the same gunman.



President Barack Obama mourned yet another mass shooting in the U.S. that he said took the lives of American patriots. Obama promised to make sure "whoever carried out this cowardly act is held responsible."