This undated photo provided by the St. Mary's Sheriff's Office, shows Deputy First Class Blaine Gaskill, a school resource officer who engaged a shooter at Great Mills High School in Great Mills, Md., on Tuesday, March 20, 2018. 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 Gaskill was credited with preventing any more loss of life. (St. Mary's Sheriff's Office via AP)