Hey everyone i'm new here and i read a lot of theories and i thought why not share my own. 
I think it's possible that everyone of the could be RJ but the most suspected are Patrick Jane, Brett Partridge and Bret Stiles, and I don't think Red John is Patrick or Bret this is why:

-Jane has an alibi for every murder. Rosalind said that he had short strait hair but Jane hasn't. Maybe it's him but he'd have to send someone to do the killings and probably Roy is just a friend of him who does some of the work. And fall in a deep trans when he kills someone and doesn't remember anything, like he has a personality disorder like in My Bloody Valentine with Jensen Ackles and everyone has to play with it.

-Bret is nothing like Jane based on Lorelei's theory and they never shook hands.

So maybe it's Brett. Patrick and him are kinda similar. The case with Kristina Frye when she was brainwashed and thought she was dead. Also Jane mentioned once that Brett brainwashes some of the Visuilise members and he knew where Kristina was. And as said maybe Roy is just one of Red Johns friends.