Well, Boo Radley kills him. However, Sheriff Heck Tate says that Bob Ewell fell on his knife because he doesn't want Boo to have to stand trial. He says it's not fair to Boo to put him out there in front of the town because Boo is mentally troubled and wouldn't good for him.
Boo Radley. the sheriff is trying to make atticus think that he fell on his knife because he doesnt want boo to have to go on trial. atticus thought it was jem but its boo