Final answer:
Jacob Roberts is the antagonist of the story as he opposes the detective, George Spinetti, presenting the classic conflict of a pursuing law enforcer and a criminal.
Step-by-step explanation:
Jacob Roberts is the antagonist of the story because he is at odds with George Spinetti, the detective on his trail. The term antagonist refers to a character that opposes the protagonist, who is often the hero or the main character in a story. In this case, while Roberts is a central character, the fact that he is a serial killer and is portrayed in opposition to the law, makes him morally reprehensible and places him in direct conflict with Spinetti, indicating his role as the antagonist.