Mafia 82. Retribution

But why isn't it mentioned whose spine Ment was twisting?

Because it's artificial.

And how do you figure out who it is out of the four?

Kosh says she's not the Mafia. That leaves Saret, Vespyr, and Heroist. Let's assume Saret is the Lord. That leaves Vespyr and Heroist. We open all the user's messages and choose the one we dislike. In my opinion, Vespyr is completely useless; she usually argues with everyone or does something else, but here she's just sitting quietly. I also remember Larisa's slip-up before her execution, about Vespyr. And there's an opinion that the Mafia targeted her, but it wasn't reflected in the newspaper; in short, they blocked her (since redirects aren't displayed anyway). This isn't an argument; the Mafia can point the finger at anyone. But nevertheless. This could mean a Servant of the Lord, isolation of the Darkness, or isolation of the Atheist (but his is very limited). Or the Clown. Or the Clown's first (?) victim, but considering it was the second day, it's still just probabilities. The Darkness's night action in the newspaper can be read, and it's clearly not isolation, one role less. However, the Servant of the Lord's night action can also be read, which means he was definitely alive at that moment.
Anyway, Vespyr's messages seem to fit the theory for me. And Heroist, as you may have noticed from the last few games, also votes for peace, so I'm considering him less.