I can't blame you for figuring things out. It is inevitable that I will die, so might as well try to get some information down.
I believe that kira is not a student, either a mafia or even a player with a role. He says he is in contact with the detective, yet the detective continues to come up with student each time? there are only something like nine students left, you would think he would find mafia some time. therefor, I think that kira isn't even talking to the detective, but using the implication of it to the same effect, then lynching off of his own suspicions, or information. Faking the detective only builds trust, then lynching from each mafia also builds even more, then you can lynch students, and proclaim it is an accident, as he has already done.
This is all speculation of course, and I ask you bear with me as I weave another possibility, mostly to the Mafia. I am quite sure kira has never been protected by the body guard. As I know for a fact that he has not been protected at key times when he was most likely to be targeted, instead, Hipmonlee was protected, this obviously incriminates me, but it might give the mafia another chance. Hipmonlee is probably a very important role, I would even guess at him being the inspector, if one is in the open. As I belive kira has never been protected, even though he begs for it, I think that he may be the body guard. His key position protects him from random killings, as he has the power of implied protection, and no one would waste a kill on that. This, of course is again speculation.