We get to know the detectives at the film's core, how they work, what drives them, and the place they're sworn to protect. And then the film ends after telling only one story, which seems kind of odd these days.
The identity of the villain is beside the point; he-she-it might as well have a Looney Tunes-ish neon arrow emblazoned KILLER! pointing at their noggin. What matters more is the thick sense of atmosphere that Mann and her collaborators conjure.
The plot is a chaos of underdeveloped relationships and frayed loose ends, but every so often, Mann does something so right that it makes this seem less a matter of narrative disorganization than a commentary on the anarchy intrinsic to any investigation.