Can police brutality be sometimes justified?

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a policeman friend of mine told me that they can't do away with it because of the limitations of the law. If a well known criminal is caught, he will most likely just post bail and get away with it. Some people are well known criminals but no one surfaces to testify against them and so they just go back to the streets. These are just some reasons why they take matters into their own hands. Are these reasons enough to justify police brutality? Why?