There are two option now: RJ is in TT brotherhood or he isn't.
If RJ is in TT organization, sheriff  McAllister is best fitted as a suspect. Even the writing on wall "He is mar" could came from "He is marshal". He is of the right age, weight, posture etc.
If RJ isn't form TT organization, then only Haffner remain. Stiles said once to Patrick he knows more then he (Patrick) or RJ could imagine, so he spoke about RJ as a third person.
My bet remains on Haffner.

PS: "Fire and Brimstone" has been the worst episode of the mentalist till now.  Nothing happened for real in it besides Patrick gathering the suspects.