Personally I think Heller is going to take each episode (leading up to 06X08 when RJ is revealed) and make each suspect look really shady. Last week it was Haffner. This week it's McAllister (from the promo video). There will then be four episodes until the reveal of RJ, with four suspects left (Stiles, Bertram, Kirkland and Smith). I don't know, they're all suspicious in their own ways. I think Kirkland and Haffner are the only viable options, but I'm fairly certain that all the suspects are connected to the case in one way or another.