Anyone who acts in a violent manner, regardless of their job or status, should be charged if they have broken the law. Police officers should not be exempt for their actions. They are there to uphold the law. If their violent actions are of criminal nature, and not justifiable to their duties and the situation at the time, they should be charged and treated the same as any other member of the public who acts in that violent manner.
I believe a lot of people have forgotten that the government works for us, "we the people". That includes our law enforcement. Our officers were put into place in order to protect and serve us. Sometimes though, you get the "bad apple" on the force. The officer that makes the other look bad. He may be violent, angry, and have a temper that seems to be invoked by the small things. If police officers are violent towards any offender that is not resisting, trying to harm the officer, another person, or themselves, that officer should be prosecuted.
It's hard to agree on when necessary force ends and police brutality begins. However, there are some cases where it is quite obvious that an abuse of power has occurred, and when this happens, the offender should be prosecuted the same as any other citizen. A badge should never be an excuse for assault and/or murder. The officers who commit these acts must be held accountable.
Each set of events related to a crime are unique and individual even if the crime is committed by the same person. While there are incidents of violence within the law enforcement community, that doesn't mean that we should judge every officer's actions by the actions of this one individual.