One other aspect that I think leads to police corruption and misconduct is the introduction of a feeling of police entitlement.  It goes without saying that it is a tremendous thing when one has the ability to take a person's life or liberty, but it is also a tremendous feeling to possess such power.  And with such a mindset, comes along that sense of entitlement - a perception that a person possesses more authentic power over others for the mere fact of being a police officer.  It is almost like a vicious, self-consuming circle.