So, I've made some points before why Haffner is looking suspicious in his first appearance (S04E02), and in his second act he continues to do.

It's the famous Red Barn episode (S05E13), and no coïnsidence our man Haffner shows again. He smells trouble, and finds a subtile reason to talk to Lisbon: he asks if she would like to start a new business with him. Maybe he's jaleous at Jane and kind of loves Lisbon (think about what Stiles once said about the patheticly jaleous character of RJ), but most of all it's kind of an excuse. In fact he wants to hear everything about the Alison farm case from her. At the end he's dissapointed the mother and daughter aren't going down for all 3 dead bodies from 1988. Probably this is a VERY lose end of his (one he not wants to be investigated further), because he was still young and careless back then - RJ in search of an identity.

Nice scene-overlap comes in the end of the episode: the daughter had a flashback to the basement of the farm and said that it felt like someone was there, someone was watching them. Next shot Haffner walks into Lisbons office (famous 'we're still friends, right?' dialogue follows).

Going back, a little earlier in the episode Haffner is so thrown off about the case that he misspeaks about Cooper who's not on the suspect-board. Lisbon is a good detective and links Haffner to Visualize immediately. Possibly she suspects him as RJ even before Jane does.


Now, of all 7 on the list I've watched their first appearence in The Mentalist and Haffner is the only one that leaves so many direct RJ-clues (indirect clues like anagrams I do not count because I catalogue them as distractions by Heller). Except Partridge, that one also bears a suspicious air around him, but I truly believe he's murdered.  

Thus Haffner's our man ;)