Complex sentence: Jill stabs Sidney in the stomach twice and mutilates herself to make it seem as if Trevor attacked her, while Dewey, Judy, and the rest of the police stumble upon the carnage.
Split into simpler sentences: Jill stabs Sidney in the stomach and mutilates herself to make it seem as if Trevor attacked her. Later, Dewey, Judy, and the rest of the police stumble upon the carnage.