When the Cop falls, he doesn't just commit a crime. He annihilates the difference between law and lawlessness. He proves that hell is not a place beneath the earth. Hell is a precinct where the lights are on, the coffee is hot, and no one is watching.
The Joker’s famous line—"Madness is like gravity. All it takes is a little push."—is the thesis of the Devil-Cop dynamic. The Cop is closest to the abyss; therefore, the Cop is the easiest to push in. The late psychologist Philip Zimbardo (creator of the Stanford Prison Experiment) coined the term "The Lucifer Effect"—the process by which good people turn evil. Zimbardo noted that evil is not a personality trait (a "bad apple") but a situational dynamic (a "bad barrel"). the devil the cop
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. When the Cop falls, he doesn't just commit a crime
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. Hell is a precinct where the lights are