I think cbi RON  is  red  john   because  :-
(1) Ron is very similar to  red john.Like R ed -jh ON.

(2) He's always there  ..behind every one   doesn't speak.As bruno heller said we've already  seen red john  many times .

(3)Red john knows everything  that happens in the cbi office. so maybe he works in the cbi office . And RJ has many times contacted jane in the cbi office  but  still he untraceable . AND  nobody can hack into cbi servers from outside.

(4) look carefully (4x13) when  RED john  meets rosalind harker.  he's sitting  like jane  and the  way  he's holding the tea cup ...just look at his hand he's wearing  a  RING  , it's blurry  but ron is also wearing same kind of ring.