Former Texas resident Aaron Alexis, 34, has been identified as the gunman who died alongside 12 others, including a police officer, during a shooting rampage at a military base in Washington.
Aaron Alexis served in the US navy reserves from May 2007 until January 2011, a US official told Reuters.
Washington’s police chief has confirmed that 12 people were shot dead and the FBI is now taking the lead in the investigation, after the shooting rampage at the Washington Navy Yard.
Police said they were looking into the possibility of two other gunmen at the scene. So far officials say there is no known link to terrorism.
Police chief Cathy Lanier said: “The big concern for us right now is that we have potentially two other shooters that we have not located at this point.
Ms Lanier said that one of the gunmen was a white male seen with a khaki tan military uniform and a beret. He was last seen with a handgun, she added.
And she said police were also looking out for a black man, approximately 50-years-old, who may have been in possession of a “long gun”. He was wearing an olive military-style uniform, Ms Lanier said.
Meanwhile Janis Orlowski, chief operating officer of Washington Hospital, told reporters the hospital was treating three gunshot victims in critical condition. One was a police officer and two were civilians.
US President Barack Obama said the United States was facing “yet another mass shooting” and vowed to hold accountable whoever was responsible.
With details still emerging about the shootings, President Obama said he had been briefed on the situation and that military and civilian personnel had been targeted.
The navy earlier said in a statement the shooting took place at the heavily guarded headquarters, where about 3,000 people work.
“There was three gunshots straight in a row,” said Patricia Ward, who works at the Navy Yard, describing how she first heard the gunfire while having breakfast at the headquarters building.
A few seconds later, Ms Ward said she heard four more gunshots.
Security guards rushed in and got people out as fast as they could – “‘Run, run, run, they told people,” Ms Ward told reporters.
Unconfirmed reports about the numbers of dead and injured came thick and fast – until Ms Lanier confirmed that 12 people were dead, one of the worst such incidents in the capital city for many years.
Dozens of police and emergency vehicles surrounded the complex in southeast Washington, which is about a mile south of the US capitol.
Helicopters circled the headquarters with some touching down on the building’s roof.
Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a hallway of their building on the third floor.
“He just turned and started firing,” Brundidge said.
Terrie Durham, an executive assistant, said she also saw the gunman firing toward her and Brundridge.
“He aimed high and missed,” she said. “He said nothing. As soon as I realized he was shooting, we just said, ‘Get out of the building.”
Rick Mason, a program management analyst who is a civilian with the US navy, said a gunman was shooting from a fourth-floor overlook in the hallway outside his office.
He said the gunman was aiming down at people in the building’s cafeteria on the first floor. Mason said he could hear the shots but could not see a gunman.
A White House official said President Barack Obama had been briefed on the shooting.
The shooting briefly shut down flights at Reagan National Airport and schools in the area.
The Navy Yard dates to the 18th century and is the oldest Navy installation. It houses a museum, the residence of the chief of naval operations and is responsible for weapons development, among other functions.