I think something was given away in the last episode...
Kirkland talked about a twin brother...could it be that at one point his twin impersonated him leading to Jane into
thinking Kirkland was a suspect?
Kirkland's brother (when he disappeared) could have left to join Visualize and at that time became Red John.
No one will suspect it because Kirkland is not one suspect but two; with Bob now dead who would think twice...