ANSWER:
If a Muslim transgresses against a non Muslim, we can’t stand there without giving the right to the victim even if he was a non muslim.
The Prophet salla Allahu alaihi wa sallam said: support your brother whether he is a victim or a transgressor.
The companions said: we know how to support him when he is a victim but how can we support him when he is transgressing?
The Prophet said: you prevent him from transgressing.