First, some people seem to think there is a disconnect between Tiger Tiger and RJ..and they may even be in opposition to each other.  I don't think that makes sense, since RJ himself quoted the TT poem.  So I think RJ is head of TT.

Later, Bertram recites part of a different Blake poem, just out of the blue.  I also think he is just playing the semi-clueless paper pusher who can't handle PJ. 

Now some people who it isn't:

Partridge - faking his death would be too cliche
Cho, Rigsby, Lisbon - What sort of huge coincidence would it be that Jane stumbled upon the CBI team that happened to include RJ.