Proposal:
The story of Robert Kirklands twin Michael, true or false, is really just a conveniently touching story of how Bob has lost a close relation to Red John, and of why his ideas of revenge are supposedly similar to Janes.

Take note that while Jane is of course trying to extract information from exposed acquaintances of Red John, Kirkland cares nothing for that goal.
Quite the opposite: He is killing them before they can talk of such matters. In other words, he is not at all trying to find or kill Red John. It is a blatant lie, misleading both Jane and the audience from the fact that Kirkland is in fact the only proven serial killer among the suspects.
Apparently Jane bought the touching story of a man seeking bloody vengeance, as he tells Lisbon then and there, that Kirkland is no longer a RJ suspect.
(Of course, Jane may yet actually hold his doubts and be playing patiently for a call of RJs suspected bluffs, such as by consciously giving an unlikely suspect the public 'honor' of being declared RJ, thereby shaming RJ into action, once more.)

Also take note that the tool Kirkland is using as a finger clipper in that scene, is the same kind of tool Lorelei was holding and getting ready to use when RJ ordered her to take of two of Janes fingers.

[This is a simplified version of theory combo 11112]