There is actually an interesting and well done Japanese drama about that subject. It's a detective story called "DeathNote", and it's essentially an allegory about god and justice.
It's about a japanese high school student with a strong sense of justice who finds the notebook of a grim reaper laying on the ground. All he has to do is write a name in it while thinking of a person's face and that person dies of either a heart attack, or whatever cause you write in the book. The student realizing what he has decides that he will make the world a better place by killing rapists, murderers, and the most disgusting elements of human society. He thinks it's a perfect crime because nobody will know he's doing it, the DeathNote leaves no traces, no evidence. But a brilliant detective, who only goes by the moniker "L" and is never seen in public, begins to pick up on the possibility that this sudden rash of deaths of prison inmates, and society's dregs may be connected. What ensues is a fantastic and interesting game of cat and mouse between a serial killer (for justice) that leaves no traces or evidence and a detective who nobody knows by name or face try to track each other down without being found out themselves.
Essentially it's an allegory with lots of biblical symbolism, it deals with the inherent problems of a single individual entity being able to decide what is moral/immoral and having absolute power in meding out punishment, and the detective "L" essentially plays devils advocate insisting that man has the ability to decide for themself without morals being imposed on them. It's interesting because it isn't arguing whether or not such a being exists, but rather would we really want a being such as that interacting with humanity? And would that being be right to do so? When the student tells his plan of making the world a better place to the grim reaper, the reaper says with a chuckle "I guess if you do that, the only wicked person left on earth will be you". It becomes a complicated question as the student begins to have an impact on society and things like crime, war, dishonest business practices begin to melt away, but at what cost?
I recomend it, it's on Netflix instant watch and on DVD if anybody is interested.