Violent Rome(1975)

Original title: Roma violenta

A detective sick and tired of the rampant crime and violence in his city, and constantly at odds with his superiors, is finally kicked out of the department for a "questionable" shooting of a vicious criminal. However, he is soon approached by a representative for a group of citizens who themselves are fed up with what they see as criminals going unpunished, and they make him an offer he may very well not refuse.