The FBI is linking a spate of shootings targeting military buildings in the Washington DC area.
In the latest incident, shots were fired at a US Coast Guard recruiting station. Four previous attacks targeted Marine Corps offices and the Pentagon.
No-one has been hurt in the shootings, which all happened overnight or in the early morning.
Andrew Ames, of the FBI, said tests had showed that the same weapon was used in each incident.
The first attack happened overnight on 16 or 17 October when shots were fired at the National Museum of the Marine Corps, in Triangle, about 36 miles (58km) south of Washington.
In the following days shots were fired at the Pentagon and then at the Marine Corps recruiting station in Chantilly.
The museum was then targeted again.
On Tuesday police were called to the US Coast Guard recruiting centre in Woodbridge where shots had been fired overnight through a window.
FBI officials say they believe the person responsible may have a grievance against the Marine Corps, as it was the target of three attacks. They have urged the person to give themselves up.
John Perren, head of the FBI's Washington office, said although the individual might not want to harm anyone, such shootings could lead to disastrous consequences.