In the novel Monster by Walter Dean Myers, how is Steve Harmon considered the protagonist and antagonist of the story?

In literature, the protagonist is considered the central figure of the story and is also the character which moves the narrative forward. The antagonist is the character that opposes the protagonist and causes conflict throughout the story. In the novel Monster by Walter Dean Myers, Steve Harmon could be considered both the protagonist and antagonist. The novel is told through Steve Harmon's perspective, and he tells the story of his trial for felony murder. Since Steve is the main character, he is the novel's protagonist. However, Steve Harmon puts himself in a compromising position in the novel by agreeing to participate in the robbery of a drugstore. Steve made a conscience decision to participate in a crime which landed him in jail, where he is on trial for his life. Since Steve made a decision that essentially harmed himself, he could be considered an antagonist. Steve also struggles to make sense of his morals and decisions throughout the novel. Steve is his own enemy because it was his decision to associate with thugs and agree to help in the robbery.