My theory is that RJ is not one single person, but a group of the high powered people we have seen in the series thus far all working together as a "hobby" and Robert Kirkland is one of them, however for the purposes of this theory I will still refer to RJ as a singular "he".
So far, RJ has outwitted local, state and national police forces - he has gone to great lengths to commit the "perfect" crimes, covered up his earlier missteps which might have exposed him, and actively sought out an opponent worthy of the name.
Kirkland is interested because even though RJ has baffled professional law enforcement, Patrick Jane has got closer on several occasions than the police ever have - Kirkland wants to know how he is doing this, and what potential mistakes Jane is uncovering in his investigations, hence the break in to copy his notes.
Kirkland killed Jason Lennon because he could identify one of the other members of the group, and that was unacceptable.
