The same gun was used to shoot at the Pentagon and the National Museum of the Marine Corps in Northern Virginia earlier this month, the FBI said Tuesday.
A third shooting occurred Monday night at a Marine Corps Recruiting Station in Chantilly, Va. Investigators are conducting ballistics testing to determine any connection to the other two shootings.
No one was injured in any of the shootings.
Investigators haven't determined a motive or identified a suspect, said Lindsay Godwin, spokeswoman for the FBI's Washington, D.C., field office.
Although all three shootings have targeted offices with links to the military, Godwin said the FBI has not issued any specific advisories or warnings to recruiting stations or other military buildings.
Early on Oct. 19, a single gunman fired multiple shots at the Pentagon. The shots shattered some windows on the third and fourth floors of the Defense Department headquarters.
Another shooting occurred two days earlier at the National Museum of the Marine Corps in Triangle, Va., 30 miles south of the Pentagon.
Federal investigators were at the recruiting station in Chantilly Tuesday, "trying to link anything they can to what has already been proven," Godwin said.
The FBI declined to identify the type of weapon or ammunition used in the first two shootings in order to avoid compromising its investigation.
Material from The Associated Press was used in this report.