It's definitely Kirkland. They shook hands, and he creepily said that he knew Patrick even though Patrick didn't know him. Plus, he just gives off a creepy vibe. Every time he says anything it's got creepy connotations. If it's not him, though, I think it might be Brett Partridge because his voice is identical to Red John's. Only problem is, they haven't actually shaken hands. Maybe it was just a metaphor for them meeting, but I feel like it would probably be literally shaking hands.