Small correction: it's neighbors, not masons. The assumption is that none of us are sure which one is scum.
Thing to note is that it won't be just the partner checking things out. The partners gets to know the deeper side of each other while the rest get to watch the person from the outside.
The typical issue with normal discussion is that the scum can claim something they really aren't or claim they did something they really didn't. A person that knows everything can catch that lie.
The issue with small groups is that it's easy to 'buddy' up and feel you want to protect your partner rather than investigate. The mass group can keep that in check.
Combine both, and we'll have things settled.
As for what to look for: My present theory is two-fold:
1. The Webadict, if there is one and I'm leaning towards there being one.
2. The weakness. Immortals have a 'buddy' that, if they die, the immortal dies. Cults have a leader that must be killed to stop the cult. The ones that died are 'anti-webadict'. I'm thinking that, along with the Webadict, we have someone pro-webadict. It's LIKE the Nuke the Nuke theory but instead of the obvious it's someone who does NOT want to die. If we kill the pro-webadict, we cut the head to the beast.
Meph (YAY two times without mispelling!) made me think of something that could be possible: Webadict could be a silent possession, or a conversion. As such the one who has it either doesn't know they have it or has no desire to tell us they have it. If it's silent, the kills might be random or set to some formula. If the person knows they have it..well.. good old SK hunting then.
However if the theory holds true, there's at least one person that may not be a killer but is anti-town and VERY self-protective.