I think you need to deal with the trauma caused by police brutality in the same way you would deal with other types of trauma. For those directly affected by police brutality, they may benefit from talking to a mental health professional to help them heal. Victims of police brutality may feel anger and resentment towards those who hurt them.
They may also develop a mistrust of police officers and the system of law enforcement. This may make they vulnerable if they are afraid to call on the police when they need them. Witnesses of police brutality may have similar reactions and would benefit from talking to a mental health professional as well.