Until Christians start reacting badly to such behavior it will continue.
Importantly, it does not have to happen a whole lot, just to establish to the Muslims that if they are abusive, or even murderous, and think themselves above the law, which is often the case; that they are *not* above retribution or vengeance by family and friends of their victims.
If several abusive Muslims were found castrated and stabbed to death after committing such crimes, word would get out among Muslims that they “shouldn’t do that”.
Certainly if some Christians were caught and punished for this, which is also likely, they would be remembered as “martyrs” of a sort, but the lesson to Muslims would still remain.
If they hire servants, it is to be servants, not punching bags who can be molested, tortured, abused and killed at will. A simple lesson. And if they don’t “get it”, then the lesson needs to be taught more forcefully.
How about they make it illgal to employ girls this young in the home?? That would be one thing. Charge this murderer and execute him too.
In real life, if this happened in a Muslim-majority area, the response would be a general pogrom against all Christians in the area, where the men would be killed and the women raped. Look up the concept of "dhimmi". A non-Muslim in a Muslim area may not raise his hand against a Muslim, even in self-defense, lest a pogrom ensue.