I just recently watched the very first episode again, and looking back, it seems very much to me like Cho could be Red John. I never noticed it at the time, because we were just dropped straight into the world, with everyone knowing each other and seemingly friends. But he seems off somehow, on second viewing, when put alongside everything that has come after. In this episode alone, he at one stage shows both knowledge of how Patrick performs his "telekinesis' parlour trick, but also a slight exasperation with it. He is similarly annoyed about Jane solving the case so easily and his theory being correct, whilst Cho's own was wrong. The biggest clues, to me though, were the fact that he was the one that called Patrick, despite him being suspended, to come down to the crime scene, the moment he and the team knew it was a suspected Red John case.
I think he did this to a) test Patrick and see if he could detect the differences and realise it wasn't a real Red John murder and b) just to see how he would react to being on a similar crime scene to his wife.
Of course, Patrick does and suspicion immediately falls on the husband----to which, Cho shows repeated, open and aloud disdain for. Even to the man's face. Watching these moments over again, it just seemed off. And maybe think that it could be a thinly veiled annoyance for the fact he believes this man is copycatting his work, a pretender. And we all know how Red John feels about people imitating his work.
I'm gonna keep with my rewatch and see if anything else stands out
