The identities of three dead Marines, including the suspected gunman, at a Virginia base will be released late on Saturday, a base spokesman said.
The shooting at Marine Corps Base Quantico on Thursday was the second fatal non-combat incident involving Marines on U.S. soil this week.
Seven died and eight other service members were wounded when a mortar exploded during a live-fire training exercise on Monday at an munitions depot in Nevada.
The Virginia shooting prompted a 3-1/2 hour lockdown of Quantico after a Marine shot dead a male and female colleague before taking his own life.
Military spokesmen declined to comment on Saturday about what motivated the shooting.
The gunman and his victims were school staff members and active-duty Marines, base commander Colonel David Maxwell said on Friday.
"This is a tragic loss for our Marine Corps family," Maxwell told a news conference.
The shooting took place at Taylor Hall, a barracks at the base's Officer Candidates School, about 40 miles south of Washington, Maxwell said. The base is known as "the Crossroads of the Marine Corps."
Base security officers received a 911 call at about 10:30 p.m. on Thursday and responded within five minutes, backed up by local police, Maxwell said. They fired no shots.
A base spokesman said the names and some information about the three deceased Marines would be released late on Saturday, following a policy of waiting 24 hours after their relatives were notified.
The Officer Candidates School provides basic instruction for prospective Marine officers. The sprawling Quantico base is also home to the Marine Corps' Brig military prison and the National Museum of the Marine Corps.