If BLM, why is it right to put a young black cop in prison for merely following orders from his superiors?

What should a cop do if his superior officer and other cops are doing something that violates protocol? Should he arrest them? Im sure Minnesota cops are not trained on such a situation. The only recourse would be to report the situation to internal affairs. Chris Dorner comes to mind. He was a young black cop who did report misconduct of his fellow officers, and in retaliation, he was terminated. Damned if you do, damned if you don't. One black man loses his life. Another black man is sent to prison for the actions of a racist white cop who should have been kicked off the force a long time ago.