Kirkland probably knows who is rj because he did not ask Lennon about him.
As rj is higher up in the system, Kirkland cant do anything to bring him down..
he might have killed Lennon because if he would have lived he would have gone to jail and rj might have freed him like he freed Martins.Kirkland ,i think, is on the good side ,he could just be saving pj by not letting him know who is rj,as pj would kill him as soon as he knows rj's identity.