Also, the child murders occurred in a triangle of local townships, which suggests the killer is working within a geographic Trinity. This plan is both conscious and unconscious, sociological and metaphysical. He buys a gas station near a lake in the mountains, the ideal location to vett possible suspects. The place is a dump, its time almost done, just like himself. Religious fundamentalism and insanity seem to go together like scotch and water.
Worship is a response to stress, the extremes of existence.
Fundamentalism always reduces the mystery of existence to a simplicity of possession and fawning contrition. Black's search for the killer is like a yearning to meet the Devil, be he God or God's antagonist. To be fair, Nicholson's character only appears to be alcoholic after the fact, even if the vibe fits the circumstances. The ending is arcane, brilliant in its symbolism and certainly daring within the Hollywood context. You won't be asleep when it comes.