The same gun was used to shoot at the Pentagon, a Marine Corps museum and a military recruiting center, the FBI said Thursday.
The conclusion was based on testing of evidence at the FBI Laboratory in Quantico, Va., the FBI said in a statement. The agency said it would have no other comment.
No one was injured in any of the shootings, which all involved shots fired after normal business hours into vacant parts of the three buildings. Investigators haven't determined a motive or identified a suspect.
Bullet holes were discovered Oct. 17 in windows of the National Museum of the Marine Corps in Triangle, Va., 30 miles south of the Pentagon. Two days later, shots were fired into two windows at the sprawling Defense Department across the Potomac River in suburban Virginia.
A third military office _ a Marine Corps recruiting station in Chantilly, Va., outside Washington _ was shot at late Monday night or early Tuesday.
Investigators haven't determined a motive or identified a suspect, Lindsay Godwin, spokeswoman for the FBI's Washington field office, said Tuesday.