According to Achille in a previous theory, we have to refer especially in the first and the 15s05, both realised by Allison Sanders.
She directed a movie named "mi vida loca" wich is the signification of a three point tattoo
It's actually a smart move and i'll follow this theory.

So i watched both of them and one character could actually fit in.
Ray Haffner is too obvious but could clearly be his right arm, mc Allister is a bit old.

I think Red John is the priest Peter Dibuono.

He own the farm in ellis county for 2 years during 86/87, he was probably one of the only people aware about the room under the barn.
His age is perfect, and he could have connection with style, haffner, he was a member of visualise.
He explain his disagreement with style and his wish to go deeper in his own research of spirituallity during his interview with Van Pelt.
He also say that he travelled a long time after he quit visualise.
That could explain why red john activities start only ten years after this first painting on the wall of the barn.
moreover, william blake is a biblical poet, john is a name of an apostle, john the red, peter dibuono, peter the good in english.

He never shake jane's hand, that could explain why he wasn't on jane's list, but they have a real connection during the episode.

Last thing, he is charismatic, smart, the director give him importance for no real reason...

The priest Peter Dibuono.