At the end of S6 E2, while listening to Sophie Miller's record, we see that all of the suspects have different sides which we haven't known. Thomas McAllister, Ray Haffner and Reede Smith, they all whistled in that episode too. This must be an obvious clue.

'He is mar'.. still may be 'He is many'. When Jared Renfrew was about to die he must have written on the wall, sth that would matter.

Consider you were killed and in your last breath what would you waste it for? For the killer for sure. Since the list was too long to mention, Brett Partridge just said 'Tyger Tyger'.(Just like Todd Johnson). This phrase must be like a symbol for Red John society I guess.

It must be a community. Then why would McAllister, Gale Bertram and Reede Smith would make that talk in S6 E2? It's getting more and more obvious that they're all involved. Working as a team, there must be only one killer since the differences on the bodies would be understood by the police. However, we aren't only looking for the killer.