Why? Because Rust Cohle has a counter-weight: He knows the Devil is real, and he hates him.
By the end, the Cop (Mills) is tricked into committing the sin of Wrath (murdering Doe to avenge his wife). The badge does not protect him from damnation. Fincher argues that to hunt the Devil, the Cop must enter the Devil’s logic. Once inside, the Cop becomes indistinguishable from the monster. Mills’ final walk away from the crime scene is the walk of a fallen soul. The uniform is just a shroud. In The Dark Knight (2008), Batman is technically a vigilante, but he functions as the ultimate Cop. Harvey Dent is the White Knight—the incorruptible district attorney. The Joker is chaos incarnate. But the Joker wins not by killing Dent, but by corrupting him. Two-Face is the Devil Cop: a man of law who now uses a coin (fate, chance, the demonic random) to decide who lives or dies. the devil the cop
Introduction: The Thin Line Between Order and Chaos At first glance, no two figures seem more antithetical. The Cop wears a badge, swears an oath to the state, and exists to enforce the mundane, agreed-upon laws of a civilized society. The Devil wears many faces—charm, scales, fire—but exists fundamentally to transgress, to tempt, and to reign over chaos. One is the guardian of the social contract; the other is the embodiment of its violation. The badge does not protect him from damnation
The horror emerges when the tester begins to enjoy the fall. When the Adversary stops serving the court (God/City) and starts serving the abyss. This is the "Fallen Cop" archetype—the inverse of the Fallen Angel. Lucifer fell because of pride; the Cop falls because of proximity to sin. Hollywood has long understood that the police procedural is a secular morality play. The detective is a priest; the interrogation room is the confessional. But the most potent narratives invert this. 1. The Devil as the Cop (The Corruptor) Consider Denzel Washington in Training Day (2001). Alonzo Harris is not a cop who made a mistake; he is a predator wearing a badge. He quotes Nietzsche and Machiavelli. He enforces a law that serves only himself. He is the Devil offering a deal: "You take the money, you let the drug lord go, and I let you live." Mills’ final walk away from the crime scene
The genius of Training Day is that Alonzo believes he is a necessary evil—that the Devil maintains order by managing chaos, not eradicating it. He is the theological argument that morality is a luxury for the weak. For a decade, he has walked the line, but the line has vanished. He is no longer the Adversary testing humanity; he is the Adversary consuming it. In David Fincher’s Se7en (1995), Detective Somerset (Morgan Freeman) and Detective Mills (Brad Pitt) chase a serial killer named John Doe who models his murders on the seven deadly sins. But the twist of the film is that John Doe is not the Devil—he is a prophet. The real Devil is the system that the cops serve.
The Cop is the Devil’s favorite disciple because the Cop has the one thing the Devil craves: Legitimacy . The Devil is a liar, an exile, a king of a kingdom that doesn't exist. But the Cop? The Cop has a badge. The Cop has the state. The Cop has the gun.
This is the moral of the genre: You cannot defeat the Devil-Cop by being a good boy scout. You can only defeat him by being a sadder, smarter, more self-aware version of him. The archetype of "The Devil and The Cop" persists because it touches a primal fear. We can accept monsters in the dark. We can accept criminals. But we cannot accept that the person with the legal right to hurt us might enjoy it. We cannot accept that the wall between civilization and savagery is a thin blue line manned by humans as fragile as ourselves.