Originally Posted by
[M] Steven Seagal
I do not think the late additions of Stallone and Diesel mean that they must be vanilla. They could be a power role, mafia, have a special role without night actions like miller or beloved princess, or be a third party role. I'm not speculating about what their roles are, just pointing out that it's not safe to assume anything yet.
Also be careful about speculating Arnolds role based on how he is playing. It's classic WIFOM.
WIFOM - MafiaWiki
He says don't go for inactives and late additions. No, it does not mean they are Vanilla. Which also means don't trust these two new people either.
He was obviously protecting Vin Diesel.
And with that said, definitely don't rule out that there may be more than one psychopath as it doesn't say serial killer so we don't know the exacts of the role. Maybe Sammy J. can shed some light on that.