I believe that Red John is an idea cultivated by a group of ex-Visulaize members. I believe Bret Stiles created a rift within the starting of Visualize and a vigilante group broke way to prove Bret Stiles wrong in some way. I do not see Bret Stiles killing anyone, but more remorseful of what has happened. So I believe Red John is an ideal more than a person or at least not a solitary person.

I also believe there are more followers of "Red John" than what the show is leading us to believe currently.