Eiji: Arrogant punk/rival guy. Not the killer, probably gets offed halfway through.
Protagonist: Not the killer, because we're seeing the story through his view. Unless they decide to do a total mindfuck ending, of course.
Wheelchair girl: Dead... but also a hypnotist. I give her equal odds of being actually dead, the killer via hypnotizing others into doing her dirty work, or innocent and hiding after making an illusion of her own death.
Matsuki: An outsider to the game. Could be the killer, given the hints in the art we've seen so far, but she has no apparent believable motives.
Tits McGee: Uhm... Has this character EVER been the killer? In anything? I exaggerate a bit, but it's usually more likely the little old lady did it than her.
Glasses guy: My immediate instinct says he's the killer, since he only shows up after everyone's been clubbed unconscious. But more likely, he's innocent and ends up being the one to get lynched.
On a final note, I find it amusing that, where in American slasher films the hot chick usually dies first, Doubt killed the moe one instead. It strikes me as a nice example of the differing ideals between cultures.