Complex sentence: Swann's father was killed by his girlfriend when he was 12 years old and his mother died when he was 16, after which Swann "fell in with a rough crowd" and began using cocaine.
Split into simpler sentences: Swann's father was killed by his girlfriend when Swann was 12 years old. His mother died when he was 16, after which Swann "fell in with a rough crowd" and began using cocaine.