Complex sentence: Adam beat Zep to death with a toilet tank cover, believing him to be their captor, but after Lawrence crawled away to get help, the real Jigsaw Killer revealed himself, and sealed the bathroom door, leaving a shackled Adam to die.
Split into simpler sentences: Adam beat Zep to death with a toilet tank cover, believing him to be their captor. However, after Lawrence crawled away to get help, the real Jigsaw Killer revealed himself, and sealed the bathroom door, leaving a shackled Adam to die.