Zametov is actually the first policeman to whom Raskolnikov confesses. Of course, Raskolnikov says he's just kidding, but this bizarre confession definitely puts Porfiry on Raskolnikov's trail.
Zametov also presents a less favorable view of the justice system than Porfiry...and that's saying a bit. Zossimov claims that Zametov is corrupt and takes bribes, and Raskolnikov sees him drinking champagne in the Crystal Palace before their little chat. Raskolnikov associates the champagne drinking with bribes and corruption—which is fair. Nothing sounds more corrupt to us than the phrase "drinking champagne in the Crystal Palace," unless it's "drinking champagne in the Crystal Palace in an offshore tax haven."