Michael Rockefeller disappeared, and was presumable killed, in New Guinea in 1961. The official cause of death was drowning (or possibly being consumed by sharks or crocodiles). Unofficially, many people have speculated that he was actually killed and eaten by a cannibalistic headhunting people called the Asmat. In Savage Harvest, Carl Hoffman travels to New Guinea to investigate the matter.
As this was an event that happened over 50 years ago in what is essentially a swamp among close-mouthed and (in the 60s) fairly primitive people, it should come as little surprise that Hoffman didn't manage to find any definitive proof. He does however dig up some fairly substantial circumstantial evidence. This includes documents from the Dutch government (who ruled the area at the time of the disappearance) and a fair amount of information on the culture and religion of the Asmat.
For readers who are interested in odd history, the grotesque, and foreign people, this is a book that's well worth reading.