Terror grips the nation's capital.
It happened at the Washington Navy Yard. Historic treasures, like cannons, used during the Revolutionary War are on display there.
Washington has been the scene of several recent terror-themed movies. White House Down, and Olympus Has Fallen both depict terrorists taking over the White House, which is about five minutes from the Navy Yard. In showtime's TV series Homeland, a sniper terrorizes the capital. And TV's No. 1show, NCIS, is set on the same naval base where Monday's shooting happened.
Experts say the navy yard is a high-security base.
Retired Senior Naval Intelligence Officer Steven Rogers showed his ID badge told Fox News, explaining, "This is a military ID card. This is how you get onto a military base. But it's not like you just show a drivers license and they flag you on. You have your photograph and your critical information on this. Then, at the rear of the card is a barcode. They scan these barcodes to verify that this is an authentic military ID card."
The gunman was shot and killed by police. But cops are looking for two possible accomplices, giving rise to speculation that it might have been a work of terrorism.
The president is vowing they will be caught. In a press conference, President Obama said, "We will do everything in our power to make sure whoever carried out this cowardly act is held responsible."