Gus cleans up the bodies, he doesn't make them. Keep the Hidden City hidden. That's the job and deal he made with one of the fairy overlords of Chicago. It's another day dismembering troll, when Gus discovers Maureen hiding out in the back of his van. His boss is hunting humans with tremendous magical potential and Maureen has already gotten away from them once.
Most people who catch the fairy's interest typically wind up on the other end of Gus's bone saw. Gus knows he should turn her in, but can't bring himself to do it. Even a man who hides the dead has a conscience. So he helps her escape, earning the wrath of the Hidden City: evil fairies, a rampaging werewolf, and a spirit assassin powered by vengeance. And that's just the start of it. His boss has gone to a lot of trouble finding Maureen the first time and will do anything to get her back. There's no way he'd both forgive Gus's betrayal and let them escape the city alive.