 Bob served as the boy's tutor in all things magical, teaching him the principles of black magic and the defense against it, and while practicing black magic is strictly forbidden by the High Council, Bob felt Harry ought to know it for "self defense".This comes into play years later when Harry, fully grown, comes back to his uncle's and discovers his father's ring and a voodoo doll.He asks his uncle if he killed his father, and Justin gives him a speech resembling a manifesto about how it's time for a change, and Justin and Harry can change things.