I think is Ellis Mars 

If RK is hunting red john why he did not just ask this to Jasson Lennon instead of kill him, after ask him 3 times if he (lennon) know who is he, RK is (must be) accomplice of RJ, think about this also, in 3x09 when todd johnson enter into the motel room and see ellis mars, why dont just kill him, remember todd is a killer with no feelings, and so more he lets ellis mars runs,a witness?? who let an eye witness just go away, also ellis mars is a "mentalist" like showing Jane he is not the only one, and mars is in the list (top 10, second place) made by Patrick Jane, remember something Patrick is a genius why consider Ellis Mars as RJ if is to simple discard him?? he has to know (or suspect) something else.