First of all , i am perfectly aware that Mashburn isn't on the list. But the fact that he was casted as "red john" on imdb.com but afterwards removed , has to mean something (tho knowing Bruno Heller it's everything but the truth lol) .. maybe just another trick.  BUT, i still think that imdb.com posted who really is RJ but BH afterwards asked for it to be removed, because they already filmed 8th episode and it was just a normal update on imdb.  
 NOW, why would possibly Walter Mashburn be red john?(I posted this theory 6-7 months ago)
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1. Since every RJ accomplice said to Patrick Jane that they are alike, they have that same charisma and a way of carrying themselfs,he is not sneaky and the kind of a creepy guy who hides in his basement. He is a good manipulator , so why would you believe anything that Rosalind Harker said? She could be  :   a) lying ( and patrick jane couldn't detect it because he always looks at people's eyes to find out whether they're lying) 
 b) it maybe true ( because Walter Mashburn fits the description, so there's that.)
(And also, i know you guys loved his character on the show ( Waler Mashburn ) which means that he has that natural way of manipulating )

2.The mentalist is not just about Patrick Jane, but also about Red John , because he is "the mentalist" too, they are perfectly alike , they are the same. So it makes perfect sense that they would get along when they meet ( not like Brett Partridge whom Patrick Jane can't stand)

3. The fact that in 6 seasons, Walter was the only one who could seduce Lisbon to sleep with him, which : a) proves that PJ and RJ have the same taste and interests.     
b) Imagine the scenario where Lisbon has to admit to PJ that she slept with the person who killed his family. I mean, it writes itself ! lol

4. Alright , this is a big one. 
Walter Mashburn while having lunch with PJ and Lisbon said that his 3. wife was all into this mystical psychic stuff.  HIS THIRD WIFE WAS CHRISTINA FRYE. 
a) She knew and was sure 100% that his PJ's daughter never woke up when RJ killed her. 
b) When RJ kidnapped her, he didn't kill her because he liked her, she was his wife . He just hypnotized her.
( PJ likes lisbon , and so does RJ. Same goes for christina , PJ dated her for a while, THIS PROVES THAT THEY ARE 100% ALIKE.)
c) final episode of 2nd. season : last thing that RJ said to PJ when he was trapped : " christina would want me to send her love , she's very fond of you despite your differences" ( like he knows christina very well and their differences.)

5. Red John didn't know patrick when he killed his family . But now when he does, he doesn't want to hurt him anymore. In his own way, he loves patrick, he wants to be his friend. 
That's why the only two people over 6 seasons that RJ spared were lisbon and christina. ( 2 women that Patrick obviously liked )

I have ALOT more to share with you.