To get right to it, I believe Michael Kirkland, Bob Kirkland's twin brother is Red John. In episode 4 of this season Bob reveals that he had a twin brother who he believes was killed by Red John. However, if you listen carefully Bob says he only believes Red John killed his brother, but in fact he doesn't know if Michael is dead or not.
Bob explains to Patrick that Michael was a drinker and nothing he did ever helped his brother recover until he met someone that saved him. Bob believes this person was Red John but I believe this person was in fact Bret Stiles.
In an earlier season Bret admits that he knows Red John and that in fact Red John was one of his followers. I believe Bret Stiles saved Michael Kirkland from his alcoholism and helped Michael to discover his true self as Red John.
A few other facts that could support this theory are that Michael is Bob's twin so Red John could easily pass off as his well connected brother Bob. Additionally, if Red John is truly a twin to Bob Kirkland then any time we saw Bob and Patrick together we could have actually been seeing Red John and Patrick meeting.
Another supporting fact is that Bob is a very smart, calculating, and detail oriented individual which stands to reason that his twin would be very much the same. We know for a fact that Red John is calculating, smart and pays close attention to the details.
Furthermore, Michael and Bob Kirkland came from a broken family with an abusive father and a mother who couldn't or wouldn't protect them because she was being abused as well. This could easily explain why Bob Kirkland had a thirst for violence and torture so a twin brother would likely be very much the same.
