Atticus appreciates what Heck Tate is trying to do, but he doesn't want anyone covering for him.The sheriff remains adamant and says that he isn't protecting Jem. That's when Atticus starts to realize that Boo Radley is the one who killed Ewell, and it is Boo that Tate is trying to protect. Then they all come to the conclusion that Ewell did fall on his won knife.