He was made a “warg”; meaning both wolf and outlaw, and became an outdweller, living apart from the rest of humanity since, by his action, he had set himself apart from normal humans. In the Volsung saga, both Fafnir and Reginn become “wargs” after they murder their father for the Rhinegold; Fafnir eventually tranforms himself into a dragon with the use of the Tarnhelm (Helm of Awe), while Reginn dwells among the Svartalfs (dwarves) and becomes one of them.
Reginn does eventually return to interact with humanity but, being a Svartalf, can never fully regain his humanness.
Both Sigimund and his son Sfinjolti live as “wargs” in the woods, shape-changing into wolves and preying on passing merchants and thanes of their enemy, Sigigaiar, husband of Sigimund’s sister Sieglinde.
Among the Celts, especially the Tuatha de Danaan, the perpetrator of a foul or horrible crime had to become that which they most feared.
In the legend of Lir’s children, their stepmother, out of sheer jealousy, curses them by turning them into swans. For her crime, the god Lugh forces her to reveal that which she most fears, which is a “Spirit of the Air” (a Bain Sidhe, or “Banshee.”) As soon as she reveals this, she is immediately transformed into one, and goes shrieking off into the night, never to be seen again.
Much of this is legend and allegory, but it does show the concept of the “warg” again, the outdweller; one that, by their actions, has trespassed beyond the boundaries of humanity and cannot return.
In actuality, greater crimes among the Celts were expiated by the laying of a “geas”, or the performance of a duty, that the criminal had to complete in order to clear his/her name. Gradually, the term “geas” came to mean “curse.”