Something else struck me:
In an EW post-S4 finale interview, Bruno Heller was asked, 'Will you cast Red John next season?', to which Heller replied, 'He might already have been cast. You might already have seen him'. If we take that as it is, the likes of Kirkland and Smith don't make sense since they first appeared in S5. However see how Heller plays with the words 'cast', 'He' and 'him' in reference to Red John: 1) Of course Red John has already been cast way back in S1, since there was or were actor/s already playing him in the few Red John scenes in S1 to S4. It follows then that 'he' i.e. Red John, has been seen by us (though never in full).
2) The question was asked if he will cast Red John in S5, so if Heller meant that he already casted THE actor to play Red John by the time the interview took place, Kirkland certainly qualifies. His statement 'You might have already seen him.' also qualifies because 'him' here would still refer to the character 'Red John', not so much the actor playing 'Red John'.
3) Heller said in the same interview that, ‘...if in season 5 we just opened a door and said “tah-dah!” and it was some mid-range actor, that would be disappointing.’ No way should Kevin Corrigan be considered a mid-range actor. If anything, he is a character actor, given his range of work. So, Kevin Corrigan coming in only in S5 to play Kirkland/Red John, makes a lot of sense. How could you be disappointed by a character actor playing the main antagonist in the story? Consequently, this possibility then disqualifies the other actors who were introduced between S1 and S4.
