Well,just finished season  4......I always had a hunch about bertram being RED JOHN specially after the poem incident where he quotes lines from the same poem i.e. William Blake's as Red John does....
Now,if you happen to watch the season finale of season 4 closely,you can't help noticing that Jane,Lisbon,Van Pelt,Rigsby and Cho are out of the question.
The final scene shows a white police cruiser speeding fast alongside Jane and Lisbon with a big bulky man at the wheels,which in my opinion,is Bertram.Zoom in and check it out.