WASHINGTON (AP) — A gunman who fired shots at a Washington-area Marine Corps museum and is believed to be responsible for three similar incidents may have a grievance against the U.S. Marine Corps, the FBI said Friday.

John Perren, the acting assistant director for the FBI's Washington field office, said during a press conference that investigators believe the person takes issue with the institution of the Marines, but not those serving in uniform. Perren said the person has gone to lengths to make sure no one has been hurt, and authorities don't believe he wants to harm citizens or Marines.

Investigators want to talk to the person and find out how to resolve that grievance, Perren said. He said the suspect may be dealing with a traumatic event such as loss of a job, financial problems or divorce.

Perren urged anyone who may have information about the suspect to contact authorities and urged people to quickly report gunfire or suspicious activity.

Someone fired shots at the museum in Triangle, Va., between 9 p.m. Thursday and 6 a.m. Friday. Authorities said that they don't know exactly what time the shooting happened, but that it appears someone fired from the side of the building facing Interstate 95.

It is the second time in less than two weeks someone has shot at the museum. Someone also recently shot at the Pentagon and a military recruiting center.

The FBI has said the first three shootings are connected, and investigators say they assume the fourth is connected as well.

THIS WAS A STORY UPDATE. Read an earlier version below.

WASHINGTON (AP) — The FBI is urging a gunman who has fired repeatedly after hours at military buildings to surrender to authorities.

FBI spokeswoman Katherine Schweit says the bureau believes the unknown shooter is hurting, but says she doesn't believe the individual wants to hurt anyone. No one has been hurt so far.

Police in Virginia are investigating an overnight shooting at the National Museum of the Marine Corps, the fourth shooting at military buildings in the Washington area. FBI Assistant Director John Perren says it bears the hallmarks of the previous shootings but authorities are trying to match the forensics to see if that's the case.

First Sgt. Kim Chinn, a Prince William County police spokeswoman, says multiple shots were fired sometime after the museum closed Thursday night.