I've been wondering if Patrick is RJ many times, but there is always one thing that makes it impossible. 
Could he kill his family? Sure. If he really is that cold-blooded sociopath, he could do it to have an excuse to join CBI and mess with them a little bit. To have fun. 
Also RJ is really great in hypnosis (which I think puts Rigsby out of equation) and as we Know Patrick is one of the best. 
But why on God's Earth would he (as RJ) rarget as a enemy number one himself??
He is messing with Jane, surely enjoys this whole game between them. What fun would be messing with himself? No fun at all.....