Hello! I would say the narrator is insane because he can still hear the old man’s heart thumping from underneath the floorboards even after he killed him. His guilt gets the better of him and he turns himself in to the cops. I don’t have any evidence sense I don’t have the story on me, but use something from the story along the lines where he “hears” the thumping of his heart as evidence.
        
             
        
        
        
<h2>Hello! :)</h2><h2 />
   There is a limited amount of information on Mayan culture because in the Common Era the Spanish instituted a policy of killing all Mayan priests and burning their books.  Catholic missionaries infact destroyed all but four of their sacred bark-paper books in the 16th century.  Information was mainly passed down through generations and generations by a highly detailed hierogliphic writing system.  
<em>Hope this helps and good luck!</em>