Honestly I am torn about who it is and regardless of my opinion I am extremely excited for the start of the season. My hunch is Brett. 

I did want to bring one thing up because others are starting to talk about it again and I haven't heard this perspective talked about.

"He is mar"

A few points:

RJ is far to meticulous to allow a nearly dead man to leave a clue on the wall. 
RJ knew, and patrick acknowledged, that Jared told Jane he would tell him who he was if Jane helped him

Mar means, "to inflict damage" or as a noun, "a blemish". I would presume that RJ wrote "he is mar". As to why, I would say RJ was explaining why he killed Jared. Or potentially being "humorous" with Jane because Jared was going to share RJ's identity.