...I see several potential anti-Town groups.
We've got pamphlets from the New Hippo League. From the pamphlets they are anti-foreigner. This makes them killers of the Dwarf, especially with the branded Hippo. But: killing one is a big step from asking the Patrician to kick them out. And besides, wouldn't (in-story) the Assessin's Guild be involved?
Secondly, we've got the group of Undeath. The sentence "all should embrace it" from the intro reeks to me of a Cult, maybe one player is DEATH or (more likely) one of the Vampires and tries to recruit others in his group?
Thirdly, there's the Omnians, worshippers of the omnipotent, omnipresent God Om. The believe system in Discworld has a specific mention of the number of members leading to the power of a god, so here's another possible Cult. They are also notoriously intolerant of others (going from the Wiki, here - my memory of Small Gods is really shady). Thus: also a good potential suspect for the murdered Dwarf. Omnianism is supposed to be a parody of Christianity, especially the worst parts, like the Inquisition - a perfect potential Scum-group, which would also fit with the "branding" theme.
Finally, we have the fights between all groups, but that just sounds like "business as usual" to me.
So, I see three potential Scum/Cult groups. With 11 players, I wouldn't be surprised to see a Cult in here. Of these potential groups, some are likely to be red herrings. Of course, they could also ALL be red herrings. After all, we're dealing with Isaac here.