A decorated military veteran opened fire at the Washington Navy Yard on Monday in a burst of violence that killed 13 people, including the gunman, and set off waves of panic at the military installation just miles from the White House and U.S. Capitol.
The FBI identified the suspect as Aaron Alexis, 34, of Fort Worth, Texas, a onetime Navy contractor who attended a Buddhist temple and had two gun-related brushes with the law.
He received a general discharge from the Navy Reserve in 2011 after a series of misconduct issues, a Navy official said.
He was killed in one of several gun battles with police.
The motive - and how he breached security - remained unknown. About 12 people were injured, Washington Mayor Vincent Gray said, though it was unclear how many of them were shot.
Hours after the incident, police were searching for a possible second suspect in an incident that raised questions about security at the Washington Navy Yard, about a mile south of the U.S. Capitol and 3 miles from the White House.
Somehow the gunman managed to enter the Naval Sea Systems Command Headquarters building about 8:20 a.m. (1220 GMT) and started picking off victims from a fourth-floor atrium, witnesses said.
It was the worst attack at a U.S. military installation since U.S. Army Major Nidal Hasan opened fire on unarmed soldiers at Fort Hood, Texas, in 2009, killing 13 people and wounding 31 others.
Hasan, who said he acted in retaliation for U.S. wars in Muslim countries, was convicted and sentenced to death by a military jury in August.