its blaitanly thomas mcallister, i can list a series of reasons. my reasons are based on the episode 'wedding in red' First off his phobia of heights which he gives away to lisbon and Jane. second his fear of pigeons, thirdly the way his voice is very much like red johns on the phone, he seems to have a sudden change in voice when on the phone to jane and then even more bizzarely he creeps up behind jane immdiaitely after jane hangs up the phone, and shows abit of nervousness around jane and comes up with the excuse of hunting when jane asks why hes right behind him. another fact is that he saves janes life makes me question thomas mcallister even more as he has previously save janes life in series 3 where red john picks jane up by the chair and says to jane 'if its one thing i wont tolerate its cheap mutations of my work' and shoots the people trying to kill jane. hes also very good at examining the body in the episode where him and jane are discussing the clues based on the body. he's very quiet at following jane around in the church and at the pond where jane is on the phone to mcallister. he seems very psycholoigcally clever the way in which he examines the body with jane aswell.
