Human nature being imperfect, corruption will exist in all human endeavors, including the law enforcement branch of government activity. Two elements of ambiguity exacerbate the difficulty of dealing with corruption in law enforcement: the ill-defined role given the police to play in a democratic society, and the contradictory nature of the laws enacted by the citizenry (which includes the public's mixed attitudes toward the law and law enforcement).
This ambiguity can be clarified by examining corruption in law enforcement in terms of levels of culpability. At the introductory, "street cop" level, basic exchanges of extra-legal amenities (free meals, discounts) between public and police straddle grey areas between corruption and common sense. At the next level of corruption, also called "graft" when speaking of law enforcement, police officers come to expect those amenities as due them. The third level of corruption finds a systematic "tradition" within law enforcement units in regular acceptance of those amenities, an extension of the street-level corruption into supervisory levels. The forth level has corruption at the street and supervisory levels set up as an organized activity: services, assignments, amenities and penalties are set up according to the schedule of the graft organization. The final level of corruption takes the police, both officer and unit, into organized, active criminal activity in direct conflict with the law enforcement mandate given it.
Corruption as a leitmotif in "expose" journalism, political posturing and genre fiction is a recurring theme bordering on the cliche. A very particular target of those seeking to expose and/or decry corruption is the law enforcement profession. It is easy to understand why: the "ground level" institution of law enforcement - the police - represents one of the most face-to-face encounters the majority of citizens will ever have with the government that rule...