I guess I know why RJ killed Partridge. I believe that along with Bertram, Smith, Mcallister, Partridge too was a member of Tyger Tyger. He might have been helpful in clearing tracks for murders committed by the members. That is why whenever we see a RJ murder, he was there. He probably knew RJ. After the list of 7 suspects was announced and Jane met with Partridge, Jane got suspicious that he might be working with RJ. That is why RJ killed Partridge so that he could not reveal Jane who RJ was. That could be the only reason why he could have been killed.

As far as RJ is concerned, he is one of the three suspects. Reede Smith would be the most disappointing. Maybe it might be Mcallister or Bertram. I know one thing for sure that the only person who matches all the criteria is Mcallister. He has been from season one and is a pretty good actor. It could be Bertram too after Mcallister, but Reede Smith is someone who cannot be possibly RJ. If Heller can prove that Smith is RJ with all the existing clues, then he is a great genius, otherwise he is just a cheater, who cheated the audience by giving them fake clues.