GREAT MILLS, Md. — A teenager armed with a handgun shot and critically wounded a girl inside a Maryland school on Tuesday and the shooter was killed when a school resource officer confronted him moments after the gunfire erupted. A third student was in good condition after he was shot.

It wasn’t immediately clear whether the shooter took his own life or was killed by the officer’s bullet, St. Mary’s County Sheriff Tim Cameron said, but the officer was credited with preventing any more loss of life.

Authorities didn’t release a motive, but said they believe the girl and the shooter — 17-year-old Austin Rollins — previously had a relationship. It wasn’t clear how the 14-year-old boy was wounded.

The officer, who doubles as a SWAT team member, was unharmed.