As a black woman I have to say that yes, without a doubt some police officers abuse their authority. Of course not every cop is evil or abusive, but if they are given the chance to some will. Whether they kill people unnecessarily, or rape people, or a lot of other atrocities.
Anyone in a position of power has a chance to abuse it, and it often happens. While not all officers do this, officers, like any person, can take advantage of the perks they are given. By nature people, especially those that take leadership jobs, enjoy having authority. The enjoyment of Authority can lead to the abuse of it.
News media sensationalizes law enforcement brutality all over because it makes for good press. People will read it. The fact is however that law enforcement constantly uses a standard of force much less than that of what they are legally allowed to use in the situations that they come upon. Furthermore with the advancement of technology in regards to cameras, gps tracking, and the like, officers are tracked much more than the average citizen. It would be so easy to catch an officer abusing their authority that it is almost non-existant except perhaps in the most rural areas of the world.