The irony of identity
The issue of identity is shown through layered narrative, because there is a story within a story, and because John Smith is given a name that misidentifies in him in some ways, because it aligns him with the European colonizers when he is actually Native American, and this puts him in an ironic position where he isn't sure who he really is, and he wants to live up to two mutually exclusive ideas about himself.
The twist on racism
This novel presents a Native American person killing white people for being white. But that isn't quite accurate; rather he is embodying a hateful narrative that his white community has taught him about Native Americans, and ironically, he embodies the wrong narrative. This shows the problem of racism upside-down so to speak, where the disenfranchisement and mistreatment of Native peoples is finally a problem plaguing white communities.
Murdering for identity's sake
That doesn't quite explain why someone would be comfortable murdering innocent people. The novel depicts the murder's motivations to be about their identity, but this is a jarring irony, because any sensible person would recognize that an identity formed out of hatred and misery cannot be a healthy longterm identity. The reader knows through this irony that the killer is a plain sociopath, regardless of how they identify.
The identity of the killer
The actual identity of the killer seems solved until John falls from a roof and the novelist (within the book) explains that maybe he wasn't the real killer after all. This ironic dilemma puts yet another twist on this story where now the reader has to interpret the killer in a more abstract, less concrete way, because there is now a question mark over John. Perhaps the killer is Jack Wilson. Perhaps the killer is just a metaphor. The reader can't be sure.
The ironic spiritualism
In the end of the book, there is a clumsy allusion to Native American spiritualism with the ironic effect that perhaps the murderer was possessed by spirits of his ancestors or the Native gods or demons or something. This adds yet another potential interpretation, but on its surface, it is an irony, because it makes the first assumption of the book (that it is about human evils like racism and murder) and dislocates them.
