Tulsa gunman bought AR-15-style rifle hours before using it to kill his former doctor, 3 others

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.