In "The Tell-Tale Heart", why did the narrator place his chair over the spot where the old man was buried when the police came?

The narrator is feeling overly confident at this point. He feels he has executed the perfect murder. The police have searched the entire house and found nothing amiss, and the narrator feels he's going to get away with the murder and the lies he's already told. He puts his chair right over the spot where the old man was buried as a symbol of his over-confidence; the police would never suspect he would deliberately sit over the spot he had hidden the body.