Oh, one other thing: Whenever the Scum team hits several power roles in a row, people always start thinking that the Scum must have an investigator. But just like with a town investigator, a scum investigator needs time to work. On the first investigation, a Scum investigator will either find a vanilla or a non-vanilla. If e finds something valuable, then the Scum team may well kill that player at the first opportunity, but it’s just as hard for the investigator to stumble across someone valuable as it is for the killer. And if the investigator finds a vanilla or someone else low-value (a weak power role, or possibly even someone who would hurt Town) on the first try, then all that tells the Scum is “kill someone other than that person”, and their chances are only slightly better than normal.
In real life, when Scum hit a lot of power roles, it mostly just means that they’re picking up hints that someone is non-vanilla, or even more likely, that they’re just lucky. Note that either of these would account for them hitting Snape (genuinely not vanilla, and luck can explain anything), whereas them having an investigator wouldn’t cast any light there (if they’d known, that’d be the last person they’d kill, just in case he decided to join them).