I am sure it is Virgil Minelli.
Miranda was killed with a fishersman's hook, and Minelli has been seen fishing after his retirement. The 5x16 character Jason Lennon(the RJ accomplice from the shelter) was also a fishermen, and tied Miranda with fishline. Minelli and Lennon met during fishing and became friends.
For me it's sure that Red John is Minelli!
