It looks like he was targeting an old girlfriend.
Via Breaking 911:
MARYLAND — Two students were shot at a Great Mills, Maryland High School Tuesday morning—the shooter, also a student, was later confirmed dead.
According to the St. Mary’s County Sheriff’s Office, the gunman, armed with a handgun, opened fire in a hallway as classes were beginning and a male and female victim were struck. The 16-year-old female victim is in critical condition and the boy, 14, was considered stable.
Officials say a school resource officer engaged the shooter, bringing the incident to an end.
The officer fired “at least a round at the shooter, and I believe the shooter also fired a round,” Sheriff Tim Cameron said at a news conference.
The shooter was identified as Great Mills High School student Austin Wyatt Rollins, 17.