Just for fun, here are some other ideas:
If we follow the
Ten Little Indians formula, Henry and Abby will be the only two left alive at the end, and each will think the other is the killer, yet they are both wrong and both survive at the end. So someone else needs to be the killer, despite everyone else apparently having been killed.
Explanation One: Someone we think is dead really isn't. The writers have been good about making the deaths un-fakeable, and/or having people around who can verify the deaths. What happened to the corpse of Maggie, the wedding planner, anyway? Can we assume the group took her body down and made sure she was really dead? She struck me as a creepy person, and I could see her having a secret affair with Wakefield and helping him with his crimes. And after all, she'd know all about those underground tunnels. I don't think survival is plausible for any of the other characters, and motive would be a big problem as well.
Explanation One-point-five: Well, we never actually
saw Malcolm being chopped up and thrown into the furnace. The bones could have been anyone's. Maybe Wakefield offered to bankroll Sacred Turtle Beer in return for assistance with various homicides?
Explanation Two: The fake-out death happens in the finale, and it's Madison, who has been surreptitiously assisting the murders. This solves the problem that the writers face in having to kill off an "innocent child," and it would be the least surprising to find out that of all the surviving cast, she is the psycho because she already acts like a psycho. And think about all the misdirection she's done: saying the sherrif kidnapped her, finding the clippings about Jimmy. Hmm. Motive? Maybe she's deranged enough to think this is all a game she is playing with her "secret friend" Wakefield.
Since this is CBS, having a likable character like Henry be the killer would be too shocking. It would be far more CBS-like for it to be Madison.