The Tribe That Hides from Man by Adrian Cowell
This is the story of a television camera crew who, in 1968, attempted to make contact with the Kreen-Akrore - the most ferocious and invisible Amazon tribe then to inhabit the rain forest. The tribe's hostility to Europeans had proved virtually implacable - for years they had been killing intruders on sight. During the 70s, as the Stone Age tribes of the Amazon fell prey to European diseases, the Brazilian government established a national park on the River Xingu, and sent out expeditions to contact the remaining Indians in an attempt to acclimatize them to the 20th century. The two Villas Boas brothers, Claudio and Orlando, were selected to make contact with the Kreen-Akrore, deep in the hostile jungle.