I know this theory would be unpleasent for the general persepctive but still I think it should be taken in consideration.

What if... Red John is not a person! but a group of persons, most likely former or current members of Visualize. A group of persons with a particular leader or such. So whenever an activity linked in anyway to 'Red John' occurs, this group plans it ahead and makes it happen. Maybe that's why 'Red John' has so many 'accomplices'. So this 'Roy Tagliaferro' might be the leader of this group, and who else is represented as leader to a group better than Bret Stiles. Although it's not likely for a young woman like Rosalind Harker to fall in love with an old man like Bret Stiles, but still he could be the master of this group and call the shots. As far as we know Lorelei Martins, Craig O'Laughlin, Timothy Carter, Todd Johnson, Rebecca, Ron Deutsch, Orville Tanner and Sherrif Hardy we're all accomplices and so, most likely, members of this group.

So here it is! let me know what you think. :D