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There will be no benefit from mutual protection of the police. In the end, they will be left in pairs and lose due to being outnumbered, right? Besides, they can be arrested/executed, as the Barbarians are easy to find. I think it's not worth removing this feature, as most likely both will check/protect or at least one of them will, because this is the path to victory, especially considering the special ability.
But the clues to find the murderers should be made more difficult, not in the style of "apple cider."
As for the mayor, it's better to remove the protection.