The Vigilante is seeing exactly what we're seeing. He can't be any more sure about someone being scum than we are on deciding for lynch.
I'm still pondering probabilities.
It's 7/10 chance to get townie and only 3/10 chance to get scum. I prefer to have more townies than less. I advocate the N-L word on Day 1 when it makes sense. However, there's a 1/10 chance of hitting the Serial Killer which could save townies from dying in future nights. Unfortunately, the Serial Killer has 1-shot night kill immunity so it would take 2 nights to kill him. Maybe the Vigilante should save his bullets after all.