Complex sentence: Patrick realised that Andy was involved in this, and set about attempting to avenge the dodgy businessman/gangster, although his prayers were answered when Andy was thrown off a bridge (to his death) by Johnny Allen, whom he'd tried to rip off.
Split into simpler sentences: Patrick realised that Andy was involved in this, and set about attempting to avenge the dodgy businessman/gangster. His prayers were answered when Andy was thrown off a bridge (to his death) by Johnny Allen, whom he'd tried to rip off.