Teen gunman in Oregon mass shooting killed three students and one teacher on school picture day as police investigate motive

The violence unfolded at 12:58 p.m., when a passing driver saw the teenager throw a 12-gauge shotgun over a school fence and climb over. Inside a special-needs classroom, a teacher threw her cellphone at the teen and tackled him.

The 16-year-old shooter at an Oregon school has been identified, though police have not revealed a motive.