It's gotta be Bertram. He quotes William Blake in season 3. Also, in the season finale of season 3 when he and Jane are waiting to "meet" Hightower he is not nervous (as Jane points out) and he seems quite content, like he knows exactly what is going on. Also, his position would explain how he always knows so much about what Jane is up to. Not to mention that he says in the latest episode "when you catch RJ, I'll be there". It's like he is taunting Jane. There is still the question of who else is involved and I don't have any answers regarding the conversation between the three suspects in Bertrams office.