Answer:
Bob Ewell wasn't killed with his own knife.
Step-by-step explanation:
Bob Ewell died as a results of being cut in the ribs with a kitchen knife. Bob attacked Scout and Jem, but Mr. Radley intervened and saved the kids. Throughout the fight, Boo Radley seemed to have stabbed Bob Ewell, causing Bob to die beneath a tree. Sheriff Tate says that Bob most likely fell over his own knife for being drunk, which makes Atticus very suspicious, since he sees that Bob didn't die from a wound of his own knife. The sheriff, then, explains that Boo most likely saved the kids and the attention that he would get from it would do him nothing but harm.