After watching most of the episodes again I am convinced that out of the 7 Haffner is RJ.

The hints at survaillence and FBI connections. Trying to manipulate Cho, offering Lisbon a new job. All things that have been discussed by other posters.

For me the thing that sealed it is the handshake. Haffner is standing atop a small mound looking down at Patrick. Trying to impose power over someone perhaps.   

At the end of it I trust the writers to deliver an epic season six. I for one cannot wait.