Did Franz Boas witness an act of cannibalism?

Franz Boas has been used as an authority for the existence of cannibalism among the Kwakiutl of British Columbia, as cited in Patterns of Culture. There is reason to think, however, that all his evidence is hearsay, and that he himself never witnessed an act of cannibalism. One indication is that he eliminated all references to such acts in his final overview, published posthumously as Kwakiutl Ethnology.