According to theology, demons and other denizens of hell can and do escape from hell. These are the creatures that have become folklore and legend in our histories. Trolls, ogers, werewolves, vampires etc. Suppose a demon (one of the most dangerous forms of demon that can shape change and lives and travels in the shadows) escaped because he was tired of living in that type of existance that he must in hell.
While he doesn't want to continue to kill and drain the life essence from his victims in order to survive, he will when he must. Choosing to select his victims from among those that prey on society.
This MAY be a good idea (or not) I really don't know how this would be accepted.