I think that RJ is not anyone from the list of seven suspects, but it's really Jane's father. He was angry that Jane ran away with his wife. After that since his main job was with Jane and his illusion tricks, So I believe that after that he went into depression and started killing people. I have little evidence of this but the only evidence is somewhat partial and it is that in a season 1 or 2 episode some Sheriff said that RJ was his dad's friend and this Sheriff was in his late 20's so RJ must be in his 50's or 60's.
Anyway it's just a theory. Hope you like it!
