It's ironic that director Damiano Damiani is most famous today for "The Amityville Horror 2", which is somewhat underrated, but no one's idea of a great movie. He has actually made any number of films in many different genres, including at least four superlative ones I've seen in just the last year: "A Bullet for the General", "The Most Beautiful Wife", "How to Kill a Judge" and this one. This is a typical Italian police thriller in some ways, but rather than focusing solely on shoot-outs and high-speed car chases, it is more of a character study of two law enforcement agents, trying to do the right thing while fighting massive high-level corruption, but in very different ways. Martin Balsam is a the titular police captain who is willing to bend the law to go after a corrupt industrial cartel leader. For instance, he gets a sworn enemy of the man and the brother of the man's mistress released from a mental institution to allow him make an assassination attempt on the crooked industrialist. Franco Nero, on the other hand, plays the by-the-book district attorney who's torn between fighting the "corruption" of the police captain and the far more pervasive high-level corruption all around him. The two eventually form an uneasy alliance.
An American film would definitely come down in favor of one man or the other (most likely the vigilante police captain), but this film is not afraid to leave the whole matter morally ambiguous. It is also pretty pessimistic in tone, as things don't work out too well for either of them. Balsam and Nero are both great (the latter was also in Damiano's "How to Kill a Judge"). Marilu Tolo (who plays the mistress) is the only other real name actor. She was kind of an enigmatic actress, probably the most Sicilian-looking actress of her era (it's hard to believe she and the blonde-haired, blue-eyed Nero are from the same country). She has a much smaller role than the two men, but still manages to transcend the usual "nice piece" mold women were usually cast in in these types of films.
Unfortunately, this is currently available only as a VERY crappy-looking public domain flick on "The Grindhouse Collection Volume 1" DVD set. (The most low-rent bootlegger would be ashamed to sell a customer a DVD-R of a video in as bad of shape and as badly ported as this one). Still if you think the price is right on the whole set or you find it from another source, this is definitely a movie I would recommend to poliziani fans or anybody else.