I've long suspected Haffner since the beginning, and many clues people here have pointed out, like him being the only suspect to call Teresa by her first name (a la RJ), or the fact that he uses his left hand like RJ, only add fuel to the fire.

One interesting thing I noticed when I rewatched the last episode Fire and Brimstone occured during the tattoo reveal scene. I noticed that when Haffner pulls down his shirt to expose his left shoulder, he does something inadvertently and/or sunbconsciously. The camera pans to him, and he doesn't just expose his shoulder like the other suspects. And he just doesn't point it out. He actually shows his shoulder, then runs his fingers in a horizontal direction, from the back of his body towards his front, where the tattoo would have been. You'll also notice that this direction corresponds to the decreasing sizes of the three dots.  It's almost like saying "see, I don't have it." He did this without seeing if anyone else had the tattoo, or even knowing what it looked like.

This is something that RJ could easily have covered, if he does in fact have it at all.

Another possible scenario is that RJ has a different tattoo at the same location as the Tyger, Tyger people, and this tattoo means that he is the boss/leader of the organization.