What seems to be motivating the killer?
Some claim that John Smith's murderous rampage is symbolic retribution for the violence Europeans perpetuated against American Indians. This is a plausible claim but perhaps more simplistic than what Alexie is trying to get at in the novel.
Sherman Alexie names the killer John Smith, likely an ironic counterpart of the Englishman John Smith who brought whites to Virginia in 1607 and interrupted the lives of the American Indians living there. Alexie's John Smith's essential, murderous rage could well be the result of being denied his ethnic and cultural identity by the well-meaning white couple who adopt him. He becomes a man without a firm identity as white or American Indian, and as his mental health becomes increasingly compromised he murders whites and scalps them, which is a custom purportedly American Indian in origin but actually often practiced as well by plenty of European colonists who took scalps as war prizes. His acts then, symbolize the overlapping mores within the realm of violence humans enact upon one another regardless of race. However, it would be an incomplete reading of Smith's character to discount the racial tensions that are all too easily reinvigorated between American Indians and whites in the twenty-first century.
The Indian Killer tells the story of an Indian serial-killer who murders white men by hunting them down, scalping them, and then finally killing them. As a signature, so no mistake can be made of his purpose, he leaves behind feathers as an indication of his Indian race. He is motivated by a blind rage and a deep racism for the white men he blames for the violent past of his people. His actions spark a racial divide in the city in which he rampages causing an uprising of racially motivated violence perpetrated by both sides.