Investigators now say that the two incidents are linked.
Law enforcement officials announced Tuesday that ballistics tests linked bullets found at the National Museum of the Marine Corps in Triangle on Oct. 17 with evidence found at the Pentagon two days later. Both buildings are within range of busy interstate highways and are about 30 miles apart.
Law enforcement officials declined to discuss the type of weapon used in the shootings or the caliber of ammunition, but they have said previously that they believe the rounds were fired using a high-velocity rifle.
The FBI's Joint Terrorism Task Force has taken the lead in the investigation. Agents are working to do ballistics testing on material found at the scene of a shooting at a Marine Corps recruiting office in a Chantilly shopping center late Monday or early Tuesday. A Marine Corps recruiter found two bullet holes in the office's windows at 8:30 a.m. Tuesday, although a Marine Corps official said the office has been closed for renovations.
Police say they are unsure what is motivating the shootings, and they are reluctant to speculate.
"We are working with local law enforcement to determine anything we can to provide us any clues," said Lindsay Godwin, a spokeswoman for the FBI's Washington field office. "I don't think at this point in time we are prepared to say this is a serial of any kind. But the targets are all blatantly military."
Although the Terrorism Task Force is leading the investigation, officials described that as a precaution because of the military targets. It is unclear whether the shootings are acts of terrorism.
The unknown shooter - or shooters - have targeted buildings late at night or early in the morning, when the buildings were either unoccupied or there was little chance of people being around. Police said that the attacks essentially amount to vandalism but that they are troubling and mysterious.