Complex sentence: Gale had found his way into the building from a backdoor entrance he slowly made his way to the back of the stage and shot "Dimebag Darrell" Abbott five times in the back of the head with a 9mm handgun.
Split into simpler sentences: Gale had found his way into the building from a backdoor entrance. He slowly made his way to the back of the stage and shot "Dimebag Darrell" Abbott five times in the back of the head with a 9mm handgun.