In a few places the writer Joseph Campbell wrote or spoke about a lurid ritual orgy that included human sacrifice and cannibalism, allegedly practiced in New Guinea. This seems to be best known from his interviews with Bill Moyers published as The Power Of Myth, but traces back much earlier to Primitive Mythology (the first volume of The Masks of God) where he reports the supposed source: Swiss ethnologist Paul Wirz who worked among the Marind-Anim people of South Papua. Here's the crux of Campbell's description from Primitive Mythology:
The particular moment of importance to our story occurs at the conclusion of one of the boys’ puberty rites, which terminates in a sexual orgy of several days and nights, during which everyone in the village except the initiates makes free with everybody else, amid the tumult of the mythological chants, drums, and the bull roarers—until the final night, when a fine young girl, painted, oiled, and ceremonially costumed, is led into the dancing ground and made to lie beneath a platform of very heavy logs. With her, in open view of the festival, the initiates cohabit, one after another; and while the youth chosen to be last is embracing her the supports of the logs above are jerked away and the platform drops, to a prodigious boom of drums. A hideous howl goes up and the dead girl and boy are dragged from the logs, cut up, roasted, and eaten.
The footnotes on this quote point to pp. 40-44 of Volume II of Wirz's Die Marind-anim von Hallandisch Sud-Neu-Guinea. I ran those passages through Google Translate and they seem to be consistent with Campbell's descriptions. The section is titled "Der Geheimkult am oberen Bian" (or "The Secret Cult on the Upper Bian").
Is there any further evidence of this practice beyond Wirz's account? Have any experts commented on its likely veracity?