His body shall not remain all night upon the tree, but thou shalt in any wise bury him that day; (for he that is hanged is accursed of God;) that thy land be not defiled, which the LORD thy God giveth thee for an inheritance.
Don't leave his body on the tree overnight; you must bury him that day. This is because anyone hanged is considered cursed by God. Doing this will keep your land, given by God, from being polluted.