A couple things one, some people are suggesting red john is a lefty because of a scene in episode one.  I believe it suggest he is a righty. Before you disagree with do an experiment take any object I used a pop can hold it in your dominate hand (most of us that would be our right) and try to manipulate with your non dominate hand it felt awkward to me.  I tried with a few other things it seemed that i naturally stabilize an  item with my nondominate hand and manipulate it with my dominate one ie hold the knife with the left clean it with the rigth.  
Another thing we should probably already know if rj is righty or lefty we have several examples of him drawing something.  A handwriting expert could tell what hand he did it with also they could probably tell if it was done by one person or several. In my opinion if reede is a lefty as suggested this eliminates him as a suspect i also believe this elimnate the idea that more than one of them has killed under the name red john (several may still be involved though)  Why think it betram I don"t know I always have thought it was from the first time he appeared Just some thoughts