An Associated Press analysis of nearly 8,000 posts from the 36 hours after the shooting shows how social media has become central to how students navigate campus emergencies. When a gunman began firing inside an academic building on the Brown University campus, students didn’t wait for official alerts warning of trouble. They got information almost instantly, in bits and bursts — through phones vibrating in pockets, messages from strangers, rumors that felt urgent because they might keep someone alive.