Ok, not a Red John theory, just a thought that seems more accurate about Michael Kirkland that some people just seem to ignore, if you think there's something off on my thought let me know please, thanks!

Michael seems to be dead, there is no way we've seen him on the show. (it's reeeeally unlikely, not impossible)

Robert Kirkland has been searching for his brother for a long time, right?
He is a Homeland Security agent, that means, he stalks and get information about anyone he wants, just like he did with Jane.

Not put the pieces together, I hope you get my point, I mean, if someone else (Michael in case) was using his name to get access to the hospital and other things, there is no way he wouldn't know it.
And therefore there is no way he wouldn't go after Michael, his vendetta is all about his brother, so...unless he was lying about something, which I find truly stupid, since his vendetta would be completely pointless.
That's why I say: there is no way we've seen Michael on the show. If indeed that was Michael at some point, then, that seems a big script failure for me, just saying.
I think Heller put this twin thing just to twist our minds and it's working (again).