Given that everyone was insane, and akrolsmir, a confirmed rolecop, confirmed he was a sanity cop, I don't think he's the killer. Since there's a lot of insane people, it's likely there were two sanity cops anyway...
So...
2. pieguy1372 <- I can't speak for you, but I know I'm not the killer
3. Rantai
4. animask <- confirmed to be sane by process of elimination (bus driver), and thus not the killer
5. foulcoon
6. rust45 <- confirmed to be sanity cop
That leaves Rantai and foulcoon. All we have to do now is lie detect something like "Rantai targeted Index-san night 1, bmin11 night 2, and akrolsmir night 3", and we'll know who it is. If you don't trust me and you want to do something like that on me, go right ahead because I know I'm innocent >.<