The most revealing episode so far has been 'The Red Barn':

1.- The detective 'Ray' whatever asks Theresa to leave CBI and join his soon to be private investigating team.

2.- He goes to Theresa and asks if the info from a certain guy helped them in the case...Theresa realizes nobody else knew about this...unless they had a connection with VISUALIZE. And so, she asks Ray how did he know about the info? He dodges with the usual 'someone in your team must of told me' crap. She continues pressuring him until he reveals he is part of VISUALIZE.

3.- He is not happy when he finds out the girl is only being charged for the murder of one guy and not the three, she presses Theresa to charge her for all three murders to which she obviously refuses.

Theresa asks him: 'Ray', if you joined VISUALIZE as a boy, then you were a member back in the 80's... Did you work in that farm back then?...'

He dodges the question right away...

So, based on that Jane found out during the episode...

A) Red John painted his signature face in the barn's outer wall, most likely after he killed the other two people and put them inside the basement.
B) Red John was a member of VISUALIZE back in the 80's...if not to this day
C) VISUALIZE is withholding information on membership lists from the 80's

So, if this Ray guy...

1) Is part of VISUALIZE
2) Was already part of VISUALIZE in the 80's
3) Shows an abnormal interest in this particular case
4) Refuses to answer Theresa's question of whether he worked at the farm during the 80's or not.
5) Knows information about the case that he shouldn't have known unless he knew it himself or was told through his VISUALIZE network.
6) Shows a keen interest in Theresa, even since the first episodes in which he appeared... coincidentally Red John is equally keen on Theresa when speaking to Jane...

Then, it is very likely he is either Red John or something VERY CLOSELY linked to him.