I'm down to 2.
My original and still current guess Bertram and then the dead man Partridge.
I want to see Partridge moaned in an open coffin, and to be sure he is dead. Otherwise all the Red Dragon and anything related to Tyger Tyger poet starts to be heavy weight resurrection evidence.

The elegance of season 3 final has left me to wonder why did Jane, by influence of RJ?, suddenly get so confident of how the room arrangement was indicated. He drove Bertram away, as a "wrong" subject.
PJ: "Walk away!"
RJ: "There will be consequences! Mark my words."

The remaining characters are just not enough "at plain sight" as these 2 have been.

I wonder why people are inclined to take on the clues which are the most concrete? Perhaps I'm too inclined to the subtle (plain at sight) clues...