There are many desirable characteristics criminal justice personnel should have. In light of this, let me name a few of them.
First, criminal justice personnel should first and foremost be impartial. They must seek to apply the law to all people without exception. So, they should treat the police as any other social group. In other words, they must not be partial to the police, as this would be some sort of cronyism.
Second, criminal justice personnel should also be courageous. They must speak the truth even in the face of opposition and unpopularity. This is an important quality to have, if one is going to oppose police corruption.
Finally, criminal justice personnel should question everything. I add this quality, because, when you are dealing with the police, that is, those who are supposed to be good, you cannot take anything for granted.