I've seen lots of people blame Marshall cause he's name start with "mar", the theoretic sentence we saw on a episode where 2 guys got killed in Mexico. If you look at the episode 1x20 you can see that the agant Marshall opens the car's door with the left hand which is pretty unusual if you look at the position he's goin (min 14:509 and we all know that Red John is left-handed (we see that when Rosaline calls Jane and John is in the background with a couple of tea) I don't know if Marshall is Red John because i personaly belive that the sentence wasn't "Mar.." but something like "na..", but i think my particualr support those theories that hink Marshall is RJ. Thanks