It seems the 1928 Dyott Expedition to search for the 1925 lost Fawcett expedition, was the first to mention the possible existence that graves of Colonel Fawcett, Jack Fawcett and Raleigh Rimmell may exist.
George M. Dyott wireless communication August 18th 1928
A film based on Dyott's exploits to find Col. P. H. Fawcett was released in 1958 called Manhunt in the Jungle, which was extended to feature length in the hopes of achieving better bookings.
Dyott's Book and a Manhunt in the Jungle Movie Poster
Perhaps it is the above report that influenced Orlando Villas Boas to go looking for Fawcett's bones, as in 1951, Orlando supposedly received the actual remaining skeleton of Fawcett and had them scientifically analyzed. The analysis allegedly confirmed the bones to be Fawcett's. But his son Brian Fawcett (1906-1984) refused to accept them. Villas Boas claimed that Brian was too interested in making money from books about his father's disappearance. However, later scientific analysis confirmed that the bones were not Fawcett's. As of 1965, the bones reportedly rested in a box in the apartment of one of the Villas Boas brothers in São Paulo.
Is this Colonel Percy Fawcett's Grave? Photo by Brian Fawcett
However, it seemed Boas was so determined to be successful in his hunt he wasn't too particular as to whose bones they were, as it was later revealed by an Kalapalo Indian named Vajuvi, that in 1951 it was Villas Boas who had approached the tribe, asking them to dig up the bones of the tallest Indian they knew, with the intent to pass them off as Fawcett’s remains.
Orlando Villas Bôas with the bones he said were those of Colonel Percy Fawcett
Although the Villas Boas 'Fawcett bones' were revealed as a hoax the hunt went on.
In 1999, the BBC broadcast a special, "The Bones of Colonel Fawcett," a segment of the Video Diaries series Benedict Allen, a self-described "maverick adventurer," filmed as he retraced the steps of Fawcett with a camcorder. Allen claims to have finally uncovered the truth by trading with the Kalapalo Indians a Yamaha 80 outboard motor for this much sought after information. The Kalapalo, with a memory that spanned 70 years, informed him that Fawcett had camped near their village and despite their warnings of danger departed the following day to continue his journey. Five days later they spotted smoke in the jungle. “They followed the trail, found where he had camped - then nothing, the forest was undisturbed," Allen said. "And that’s all they said they knew about Fawcett. They wouldn't speculate further. The inference is that they were killed by other Indians. At the time there was a group called the Iaruna, who had a raiding party sweeping through the area.”
This information hardly seems worth the cost of the outboard motor given as reward for the tale, although I very much doubt the Kalapalo were complaining.
The Kalapalo chief, Vajuvi, then showed Allen the site of the grave from which Fawcett's alleged bones were taken. The bones given, (no doubt at a price) to Orlando, he said, were actually those of his grandfather because he was unusually tall for an Indian.
To date no evidence has been discovered of the remains or the last resting place of Colonel Fawcett, Jack Fawcett and Raleigh Rimmell. It is possible, however unlikely, that one day their bones may be discovered. If they are and depending on their condition, a forensic examination should be able to reveal how they died.