Okay, we've all filed through the evidence hundreds of times and all come up with some very good theories based on the facts.  For me, the following is my evidence:

1.)  He Is Mar = He Is Marked:  The tattoo is legit.
2.)  Hunter Ethos:  We know he'll hunt "anything with a face"
3.)  Handshake Theory:  I theorize the handshake had to be on screen.  Their "shaking" of hands was by playing rock, paper, scissors.
4.)  Physical Profile:  6 years ago, he had short-straight hair.  He's under 6 ft, rough strong hands,   not muscular but not soft.  Probably smells like the woods "pine and earth", middle-aged, in good health.  Good posture, self-possessed.  Has a phobia: Orinithophobia, fear of birds.
5.)  Well-placed job:  He is less-confined by his work, spends many hours alone away from the public eye.  His car and profession could easily trick his victims into trusting him.
6.)  Friendliest:  Of all the suspects, he's the only who gets along with Jane.  Also only calls him "Patrick".

I feel those are strong arguments, but the strongest I have is simply the chemistry between McAllister and Jane.  It is by far one of the most intriguing dynamics of the group.  Jane went to Napa to get to know him better.  I have a feeling, McAllister barely made the list.  Patrick probably thought he was possible but unlikely.  However, when he went to meet him, I believe Jane saw a darkness in him, a "blood lust".  He took a little too much pleasure in shooting Jane's kidnapper.  "Now he's talking directly to Jesus".  Plus he has an intelligence, stealthiness and charm that truly fit RJ.  

When the Sheriff showed his tattoo, it seemed like Jane was expecting it to be him.  All the pieces fit.  He thought he had his man, but low and behold, Bertram and Smith had the same tattoo.  Next episode, he'll hunt down Bertram and Smith, but they will not be RJ.  The Sheriff will have faked his death and still be at large.