Season 4 Finale : 

Red John : Oh, you strung me along for a good long while. Congratulations. Fortunately, I have a friend in the FBI, so I found out when the FBI found out.

Season 5, Episode 5 : 

Schultz : I would like some updates on the Red John Case...
Minelli : To put it bluntly Alexa, why would I do that??? What's in it for me ???
Schultz : Well, it's always good to have a friend in the FBI, isn't it???

Also, I believe Tommy Volker could be a friend of Red John (Not accomplice, a friend)