A nightmarish scenario almost went from bad to worse at Great Mills High School in St. Mary’s County, Md., but for the quick action of school resource officer Deputy 1st Class Blaine Gaskill, armed and stationed inside. Gaskill pursued and fatally wounded a student who had shot and injured two of his schoolmates before he could do any more harm.

According to NBC Washington, Austin Wyatt Rollins, 17, brought a semi-automatic handgun into the high school shortly before 8 a.m. on Tuesday and opened fire in the hallway, wounding a 16-year-old female and a 14-year-old male student. Rollins then shot at Gaskill before he fired a round at Rollins, fatally wounding him.