WASHINGTON — As many as two gunmen opened fire Monday morning inside the Washington Navy Yard, killing at least 12 people in an attack on office workers at the heavily secured military installation in the heart of the nation's capital, authorities said.
One gunman was dead, and police hunted for a second possible attacker who may have been disguised in a military-style uniform, police said.
Investigators said they had not established a motive for the shooting rampage, which unfolded less than four miles from the White House. As for whether it may have been a terrorist attack, Mayor Vincent Gray said: "We don't have any reason to think that at this stage."
The FBI took charge of the investigation.
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."
The area that was targeted, known as Building 197, was part of the 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.
Around midday, police said they were searching for two men who may have taken part in the attack — one carrying a handgun and wearing a tan Navy-style uniform and a beret, the other armed with a long gun and wearing an olive-green uniform. Washington Police Chief Cathy Lanier said it was unclear if the men were members of the military.