If you use your instinct instead of only clues (that are read hearings most of them) you will see that RJ was revealed a long time before.
I admit I was fooled by Heller, until last episode (7) where in the final was so obvious who RJ is, if you just clean your mind and watch the last episode you will see the same..

Reviewing some of what Sophie said about RJ:

"He's well spoken, good posture,self-possessed, in the waiting room he sat calmly...he says he deals with conflict and adversity easily, though I am not convinced he is being truthful about this...In fact much of what he said though spoken convincingly, did not match what i can only call my instinctive response to his presence...I sense something deceptive and dark in his emotional makeup..."

Now in your guts, which character does this description fits the most?

Every other suspects than Gale fail in some of this points. Macllister is not self-possessed enough, not even Haffner, Reed doesn't have a good posture and it's not exactly well spoken, Bret posture it's also not that good.

"deals with conflict and adversity easily, though I am not convinced he is being truthful about this.."
He is proud, but likes to pretend is not..he is proud enough to kill PJ family just because he humiliated  him on TV...who is the show off guy there? 

 "sense something deceptive and dark in his emotional makeup..."
This is the most important characteristic, watch closely Episode 7. Watch closely each suspect eyes and manners, specially after PJ revealed the tattoo thing. 
Gale was so obvious it hurt's..his emotional backup was fallen..the darkness in his eyes, his expression, the way the camera filmed him..

It's Gale 100% sure