More than a year ago, tips about online posts threatening a school shooting led Georgia police to interview a 13-year-old boy, but investigators didn’t have enough evidence for an arrest. On Wednesday, that boy opened fire at his high school outside Atlanta and killed four people and wounded nine, officials said.The teen has been charged as an adult in the deaths of Apalachee High School students Mason Schermerhorn and Christian Angulo, both 14, and instructors Richard Aspinwall, 39, and Christina Irimie, 53, Georgia Bureau of Investigation Director Chris Hosey said at a news conference.At least nine other people — eight students and one teacher at the school in Winder, about an hour’s drive northeast of Atlanta — were taken to hospitals with injuries. All were expected to survive, Barrow County Sheriff Jud Smith said.The teen, now 14, was to be taken to a regional youth detention facility on Thursday.Armed with …