Then, Night 2, two kills must have happened from unexplained sources, and the kill on X must have come from Purple Mafia. Brutus would then be using that kill to evidence his fake claim, outing himself to the purple Mafia.
I obviously do not think this scenario is likely as it would mean Brutus elected to shoot PoE slot Sera last night just to prove his claim. So I am not arguing that this is what happened. Just that this scenario is how he could be scum. I'm actually arguing it to refute the notion that he's scum, as I find the scenario rather ridiculous. Let me know if you have any questions about this still.