The man accused in a shooting rampage at a US navy base has been identified as a man from Texas.
A federal law enforcement official said Aaron Alexis was 34 years old. He is believed to have a criminal record and to be a holder of a concealed carry weapon permit.
Alexis is believed to have gotten into the navy yard by using someone else's identification card. It is not yet clear if that individual was an accomplice or if that person's ID card was stolen.
Earlier, police said at least 12 people had died in the shooting rampage at the navy yard in Washington DC.
One gunman had been killed but police warned there were possibly two others still on the loose. One officer was shot in a gunfight with one of the men. Both the remaining suspects, one black, one white, were wearing military-style uniforms although they were not believed to be serving troops.
Police Chief Cathy Lanier confirmed the death toll during a news conference. She said people were being told to stay in their homes and out of the area as authorities search for the suspects. There was no indication of a possible motive, she added.
The shootings happened inside one of the Navy's oldest buildings, targeting office workers at a heavily guarded military facility in the heart of the nation's capital. The attack unfolded just a short distance from the White House and the US Capitol at a former shipyard that is one of the navy's oldest shore facilities.
President Barack Obama mourned yet another mass shooting in the US that he said took the lives of American patriots. He promised to make sure "whoever carried out this cowardly act is held responsible."
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.Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a long hallway on the third floor. The gunman was wearing all blue, he said. "He just turned and started firing," Mr Brundidge said.