It shall be, that he who is taken with the devoted thing shall be burnt with fire, he and all that he has; because he has transgressed the covenant of Yahweh, and because he has done folly in Israel.
The burning of a criminal after his stoning was one way of emphasizing the wickedness of his crime (Leviticus 20:14; cf. Deuteronomy 13:15-16). It was a "disgraceful thing" (Joshua 7:15) to steal something under the ban (devoted to God).