I would primarily suspect anyone who has been too quiet, or too unhelpful. Going through a list and seeing whose faces stand out would not go amiss. Which ones would you expect to be doing more than they are? Which ones seem to derail the discussion? Do these actions feel in character, based on what we know?

Secondarily, I would question the motives behind the choice of Dipper and Mahiru. It didn't seem like an obvious pick to me. However, Mahiru was working with Miss Shameimaru on her newspaper, and Dipper was heavily involved in investigating the crime scenes. Either of these could have been the source of the threat.

Finally, I would be concerned about the situation with Levi yesterday. Wasn't it a little inconvenient the dog stayed misinterpreted until after Levi's death? Wouldn't it have been all to easy to deliberately waste the afternoon and put off Missile's reveal? After all, if we'd known Edea was guilty yesterday, I certainly would have elected to vote for her instead of Levi. And it's not as though the dog could reveal anything.

That would be my line of analysis.