Okay, so there are a few reasons that could explain dsister's behavior.
1. He's Kira, trying to get investigated so that we think he's innocent.
2. He's a Kira supporter, trying (and failing) to do what zexen did in the last Death Note game.
3. He's a townie who's lost his mind.
4. He's L and wants the doctor to notice him and protect him.
Honestly, I doubt that number 4 or number 2 are right. If he was a Kira supporter, he shouldn't just give himself up so soon. Of course, it seems really stupid that he would be Kira himself since he's drawing way too much attention to himself. In the last game, Son1x lived simply by voting with everyone else. He barely posted. It doesn't make sense that if he was Kira, he would be drawing so much attention to himself.
As of now, I'm inclined to believe that he's just lost his mind. Unless That Guy threw a Jester role in the game... (The Jester is a role where you win if the town lynches you).