A Marine shot and killed two others and then killed himself Thursday night at Marine Corps Base Quantico.
All three were staff members at the Officer Candidates School at the base in Viriginia, authorities said.
A relationship dispute is believed to be the cause of the shooting, reported News4 Northern Virginia Bureau Chief Julie Carey. The dead were two men and a woman.
Police responding to reports of shots fired just before 11 p.m. initially encountered one victim and the shooter, who fled into a barracks, base commander Col. David W. Maxwell told reporters in a press conference.
When authorities entered Taylor Hall, which houses staff at the school, -- they found the shooter and the second victim.
The names of the dead will not be released until the next of kin are notified, Maxwell said.
The base was locked down during the investigation. However, authorities said the shooting only involved the school. "This is an isolated incident," a Marine Corps official said.
The base reopened early Friday morning.
In a statement, Pentagon press secretary George Little said Defense Secretary Chuck Hagel was saddened to learn of the shooting.
"This tragedy, as well as the tragedy in Nevada earlier this week, took the lives of Marines who volunteered to serve their nation," Little said. "His heart and his prayers are with them and their families."
The shooting is the second tragedy the Marine Corps has faced this week. Seven members of the 2nd Marine Expeditionary Force were killed Monday when a mortar shell exploded in its firing tube during an exercise at Hawthorne Army Depot in Nevada. Eight others were injured.
Maxwell seemed emotional in the press conference, apparently choking up as he discussed the events.
The Quantico base, which is about 37 miles south of Washington, is also home to the FBI's training academy. Its Officer Candidates School is the equivalent of basic training for Marines interested in becoming officers.
According to a Marine Corps website, the mission of Officer Candidates School is to train, screen and evaluate candidates. The training includes both academics and physical training such as endurance hikes and obstacle courses. Marines become second lieutenants on graduation from the 10-week program.
The Associated Press contributed to this report.
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