First of all. I just want to criticize some theories that have come up on this site. 
Red John is not Bob Kirklands brother. Red John is someone on the list. He is asking if the suspects recognize him because it was his twin brother that Red John murdered. 
Red John is someone on the list. Heller has confirmed it several times. It's someone of the guys. It's the real cards on the table. It's not Alex Jane that has gotten a plastic surgery neither is it CBI Ron or Patrick Jane himself. It's unlogical, contradicting and would not fit in with the Mentalist-mystique. Those who have watched this show long enough and in detail knows this. 
Red John is most likely somewhat associated with the "Tyger Tyger-Conspiracy". It's not likely he is not. Of course he is. Why would he have first read the Blake poem to Patrick if not? A coincidence? No. That's really phony. 
Then who is Red John?
Ray Haffner, I would say. He has the right looks, the right age, he Visualize-connections and of course he is a good actor. He has the right level of creepyness to. I hope it's him, although I'm not sure at all. It could be anyone and if we know Bruno Heller we could be up for another crazy twist. 
I wish for Red John being a singular individual. Something else would be disappointing. 
Cheers.