I believe that the show is gearing up towards a reveal of Bertram. However, based on other clues, I think some other ideas work better:

McAllister: born in 62-3, would make him 25-6 in 88, i.e first killing when he was an adult. He also would easily smell like pine, per Rosalind. Boots may be a hint.

Haffner: Better association with Visualize, and being born in 1967, he would be 21 in 88, so maybe the barn killings were a rite of passage.

I think at this point we have to assume "he is mar," is he is marked. With the PJ and RJ relationship innuendo's I have no problem thinking that while not sexual, perhaps RJ does take off his clothes to kill.

Bertram does fit in with "Cold" as per the Wikia explanation, but I think there is a better solution there. I hope we get some flashback episodes to explain it all.