A man who shot two police officers at an underground station near Washington DC that serves the US Department of Defense has died, police have said.
Patrick Bedell, 36, from California, was shot in the head in the incident at Pentagon Metro on Thursday evening.
The two officers, who were grazed by bullets, were treated in hospital.
Police said they had found no immediate connection to terrorism, but internet postings suggested Bedell had harboured ill-feelings towards the government.
A user by the name of "JPatrickBedell" wrote that he was "determined to see that justice is served" in the death of Marine Col James Sabow, who was found dead at his California home in 1991.
The Associated Press news agency said that death was ruled a suicide, but the case has long been the source of theories of a cover-up.
The posting referred to conspiracy theories concerning the 9/11 terrorist attacks, saying the Sabow case was "a step toward establishing the truth of events such as the September 11 demolitions".
Pentagon police chief Richard Keevill said Bedell had given no clue to the officers at the entrance to the underground station about what he was going to do.
"There was no distress," he told reporters. "When he reached into his pocket, they assumed he was going to get a pass and he came up with a gun.
"He wasn't pretending to be anyone. He was wearing a coat and walked up and just started shooting.
"We have layers of security and it worked. He never got inside the building to hurt anyone," the police chief said.
Mr Keevill said it appeared that Bedell had acted alone.
Afterwards, all entrances to the Pentagon were secured. All were later reopened except one from the station, a spokesman said.