I wish to present two ideas:

1. I think we shouldn't arrive in a judgement regarding any of the suspects based on the characters portrayed to us so far. If RJ is one of those 7 - and Heller confirmed he is - I think what we saw so far of that character may have simply been a deceitful act. 

Take Reed Smith, based on his character as it was portrayed to us, none us would consider him RJ material. But if the Reed Smith we know is simply a facade,  meant to deceive every one. Maybe that's what RJ does to hide himself, present himself and perform as a mediocre hot head.

In fact, up until Bret Partridge was slayed by RJ, I thought he could be RJ not because he is weird and has a psycho feel around him, but because Heller portrayed him to us as a youngish, not very charismatic figure, again not really RJ material, if you will.

I think that may be what Heller meant when he said we will be disappointed when RJ is revealed. So I'm thinking: which of the remaining 6 suspects would be most disappointing, if you will, based on the character portrayed to us so far? I think Reed Smith. So maybe Reed Smith is the facade RJ uses.

2. Another reason why I previously thought Bret Partridge may be the one was the tender voice fit the RJ as we heard speak. 

But now Bret Partridge is gone, there is no other suspect whose actual voice sounds anything like what we heard from RJ in those few scenes. Now I believe that RJ used some kind of voice alteration device during those encounters.