(CBS News) A Marine who worked at a rigorous school that tests Marines who want to become officers fatally shot two of his colleagues before killing himself in a barracks dorm room.

The three Marines — two men and a woman — were part of the staff at the officer candidates school on the sprawling Marine Corps Base Quantico in northern Virginia. Their relationship and whether they knew one another was not clear, though military officials described the shootings as “isolated.” They did not release the identities of those slain.

CBS News correspondent Bob Orr reports from Quantico that no motive has yet been established or released by authorities.

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