After having reviewed the background appearances of the Red Sweater man (http://www.youtube.com/watch?v=590v4FCm6WU), I feel like he could turn out to be RJ after all. In that scene the man pretending to be RJ talks about changing his identity and making a new life. Then, in season five we get Bob Kirkland, who looks allot like Red Sweater Man. I know that there are a couple of clues that would seem to disqualify Kirkland, but like the murder suspect in many episodes over the years, they could easily be explained. among the seven suspects, none act more like a serial killer than Bob, and he has also proven hat he has no problem with murder.
He may turn out to only be a RJ soldier, but he seems like the most likely suspect to me. I'll be disappointed if it's Haffner, if you look at his first show he in no way seems like RJ: both in his interactions with PJ and the way Bertram talks to him.