Three staff members of the U.S. Marine Corps Officer Candidates School are dead after one of them opened fire on the other two late Thursday before committing suicide, military officials said early Friday morning.

The shooter and the victims have been identified only as two men and a woman; one of the men is considered the sole attacker. Military police and officers from the Prince William County, Va., Sheriff’s Department responded around 11 p.m. EDT Thursday night to what is believed to be an isolated incident.

"There was nothing random here,” an unidentified officer told NBC, suggesting the shooter specifically targeted his victims. He then barricaded himself inside a barrack, which was breached by the authorities around 3 a.m.

The identities of the victims will be released after the next of kin have been notified. The base was operating under “Code Green” status Friday morning, meaning a lockdown that was initiated after the shooting broke out had been lifted.