Updated

A U.S. Marine who shot two of his colleagues to death and then killed himself was a tactics instructor at a school that tests Marines who want to become officers, military officials said Saturday.

Sgt. Eusebio Lopez, 25, gunned down 19-year-old Lance Cpl. Sara Castromata and Cpl. Jacob Wooley, 23, on Thursday night inside barracks at the Marine Corps Base Quantico south of Washington. Other than to say the three Marines worked together at the school, military officials have not described their relationship or released a motive for the shooting.

Lopez was a teacher whose specialty was machine gunner. He joined the corps in May 2006 and deployed in support of the wars in Iraq and Afghanistan.

Castromata was a warehouse clerk who had been in the Marines since December 2011. Wooley was a field radio operator. He joined the Marines in February 2010.

Lopez was an instructor at officer candidates school, known for its grueling 10-week program that evaluates Marines on physical stamina, intelligence and leadership. The candidates must complete obstacle courses, hikes in full combat gear and take classes on navigation and tactics that help them in the field, according to the school's website.

Lopez's great-grandfather, also Eusebio Lopez, said the Marines contacted their family on Friday night.

"They told us they were investigating more, and they'd let us know. He wasn't the type to do stuff like that," said Lopez, 81.