Complex sentence: To his horror, Boone is informed by Decker that he is responsible for brutal mutilating murders of eleven people, murders that have been committed by a serial killer and have terrorised the city of Calgary recently.
Split into simpler sentences: To his horror, Boone is informed by Decker that he is responsible for brutal mutilating murders of eleven people. On top of this he is informed he is responsible for murders that have been committed by a serial killer and that have terrorised the city of Calgary recently.