A gunman who killed four people at a Tulsa hospital Wednesday targeted a doctor who had treated him and bought the AR-15-style rifle used in the shooting on the day of the attack, police said. Michael Louis was armed with a rifle, which he had purchased at 2 p.m. Wednesday, and a handgun when he went to St. Francis Hospital shortly before 5 p.m., officials said. He opened fire inside the Natalie Building, killing Dr. Preston Phillips and Dr. Stephanie Husen, receptionist Amanda Glenn and a patient, William Love, police said at a news conference Thursday. Tulsa Police Chief Wendell...