Unlike some films (here’s looking at you, The Usual Suspects), Frailty holds up very well on a second viewing, probably because there’s more to it than just the twist, like the honest depiction of emotional abuse and the culmination of the film’s cynical journey towards its gut punch reveal.
You refer to McConaughey’s Adam as the God’s Hand killer, but he explained that was Fenton. The God’s Hand killer left notes, which is how the FBI knows to attribute his victims to him and got the name to refer to him by. Adam has even more victims, but the FBI is unaware of them. And since he doesn’t leave notes (and frames Fenton for the FBI agent he kills), the authorities will continue to overlook him.
You refer to McConaughey’s Adam as the God’s Hand killer, but he explained that was Fenton. The God’s Hand killer left notes, which is how the FBI knows to attribute his victims to him and got the name to refer to him by. Adam has even more victims, but the FBI is unaware of them. And since he doesn’t leave notes (and frames Fenton for the FBI agent he kills), the authorities will continue to overlook him.