Rough estimates have put the Sentinelese population at between 50 and 150, and they have their own language which is not spoken by any outsiders, and is unrelated to those on surrounding islands. They concluded that it had to be Chau.
After his kayak became damaged on 15th November, he swam to the fishermen's boat, which was waiting at a prearranged location and spent the night there, writing out his experiences on pages of paper which he gave to the fishermen, police said.
A statement issued by the police for the Andaman and Nicobar islands late Wednesday said the police and India's coast guard carried out an aerial survey of Northern Sentinel Island on Tuesday.
"It's a hard proposition", said Dependera Pathak, director-general of police on India's Andaman and Nicobar Islands, where North Sentinel is located.
"We are aware of reports concerning a USA citizen in the Andaman and Nicobar Islands", a spokeswoman for the United States consulate in India's southern city of Chennai said in an email.
The tribesmen who killed John Allen Chau, an American missionary who wanted to convert a protected Andamanese tribe to Christianity, must be forgiven, the family of the 27-year-old man said in an emotional message.
"God, I don't want to die", were among his last words.
They said "words can not express" the sadness they are experiencing, adding: "We forgive those reportedly responsible for his death".
In 2004 a helicopter that was sent to check if the tribe had survived the Boxing Day Tsunami was pelted with rocks and arrows by members of the tribe. Go2Andaman describes the island as the "hardest place in the world to visit".
Seven people who helped him reach North Sentinel island have been arrested.
Tourist Killed by Arrows After Trying to Convert Indian Tribe to Christianity
A SWASHBUCKLING American preacher outlined his weird plan to convert the world's most isolated tribe to Christianity in a series of handwritten notes made public by his family.
On the morning of November 17, the fishermen saw a dead person being buried at the shore, presumably by the Sentinelese tribe people.
"Don't blame them or God if I am killed", he wrote.
The Sentinelese people are highly resistant to outsiders and the government tightly restricts visits to the island.
"He didn't go there for just adventure".
Mr Chau also worked with Mr Parks' non-profit organisation, More Than a Game, a soccer program for disadvantaged children, including refugees.
"The Indian government has adopted an "'eyes-on and hands-off' policy to ensure that no poachers enter (North Sentinel Island)", according to India's Ministry of Tribal Affairs. According to The Post, "Chau's riveting journal of his last days shows a treacherous journey by dark in a small fishing boat to the area where the small tribe lived in huts".
There is also a possibility that the islanders were angry that he had set foot on the island by bribing fishermen to ferry him through.
Another group in the Andaman Islands, the Jarawa people, are also hostile to outsiders, but their future is under threat from a highway which runs through their territory.
The authorities said Chau arrived in the area on October 16 and stayed on another island while he prepared to travel to North Sentinel.
The Sentinelese are estimated to number about 100 and are the most isolated of the four tribes that are native to the Andamans. The source said Chau had taken scissors, safety pins and a football as gifts to the tribe to try and establish a rapport.
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