So im gonna go with what I consider obvious.
Bertram, Smith and McAllister are part of this big organization that involves police, fbi and who knows who else, so im gonna go with the theory that Red John is not ONE person, but a bunch of people.
Think about it, just like "Hostel" bunch of crazy people who like to kill just for fun so they created this "club" so they can cover each other when they do it.