An American who ignored laws preventing outsiders from visiting an island where the indigenous people are protected has been killed by its inhabitants.
John Allen Chau is said to have died in a hail of arrows as he set foot on North Sentinel Island, part of the Indian-controlled Andaman Islands in the Bay of Bengal.
The people who live there are one of the few tribes completely cut off from the rest of the world and have previously fired at outsiders.
Indian police officials confirmed the death and said a local electronics engineer simply named Alexander, who was a friend of Mr Chau's, a local watersports instructor and five fishermen who allegedly aided last Saturday's visit have been arrested for violating the terms of the island protection laws and for causing Mr Chau's death.
An Andaman and Nicobar Police statement said Mr Chau, 27 - who described himself as "an explorer at heart" - had hired a fishing dinghy to get close to the island, before changing to a kayak they towed behind the boat.
"He was attacked by arrows but he continued walking. The fishermen saw the tribals tying a rope around his neck and dragging his body," an official source told the AFP agency.
"They were scared and fled but returned next morning to find his body on the sea shore."
In the statement, police said Mr Chau's friend and the water sports instructor put him in touch with the fishermen in Port Blair on South Andaman Island who he paid about 25,000 rupees (£275) to get him close to North Sentinel Island, despite tourists being banned from getting within three miles of the island.
The Sentinelese, with an estimated population of between 40 and 200, are said to be at risk of death if they have contact with outsiders as they have no immunity to common diseases like flu and measles.
On the evening of 14 November the group of six pretended to be fishing to evade the patrolling police, coast guard and navy ships, reaching the island at midnight before Mr Chau kayaked to the island on the morning of 15 November.
Police said the fishermen agreed a time and place to meet each other near the island.
On the morning of 17 November they saw "a dead person being buried at the shore which from the silhouette of the body, clothing and circumstances appeared to be the body of John Allen Chau", police said.
Local officers said they received an email from the US consulate general in Chennai, on the Indian mainland, saying Mr Chau's mother had contacted them to tell them he had visited North Sentinel Island and been attacked by tribesmen.
They said the fishermen informed Alexander in Port Blair about his death and gave him 13 pages of his journal. Alexander then told one of Mr Chau's friends in the US who told his mother.
"They didn't inform the police or any government authority in this regard," Andaman Police said.
The US consulate in Chennai said it was aware of the reports of the death but a spokeswoman declined to comment further.
Police officials said a murder case had been registered against "unknown" tribespeople - but they are also blaming the fishermen, Mr Chau's friend and the watersports instructor.
Andaman Police added: "Despite knowing fully well about the illegality of the action and the hostile attitude of the Sentinelese tribesmen to the outsiders, these people collaborated with John Chau for this visit to North Sentinel Island without any permission from the authorities."
Two Indian fishermen were killed on the island in 2006 when their boat broke loose and drifted onto the shore.
Poachers are also known to fish illegally in the waters around the island, catching turtles and diving for lobsters and sea cucumbers.
Stephen Corry, director of Survival International , which campaigns on behalf of indigenous people, said: "This tragedy should never have been allowed to happen.
"The Indian authorities should have been enforcing the protection of the Sentinelese and their island for the safety of both the tribe and outsiders.
"Instead, a few months ago the authorities lifted one of the restrictions that had been protecting the Sentinelese tribe's island from foreign tourists, which sent exactly the wrong message, and may have contributed to this terrible event.
"It's not impossible that the Sentinelese have just been infected by deadly pathogens to which they have no immunity, with the potential to wipe out the entire tribe.
"The Sentinelese have shown again and again that they want to be left alone, and their wishes should be respected.
"The British colonial occupation of the Andaman Islands decimated the tribes living there, wiping out thousands of tribespeople, and only a fraction of the original population now survive. So the Sentinelese fear of outsiders is very understandable."
Andaman Police said they joined the Indian coast guard on Tuesday in carrying out a recce of the island from the air and on Wednesday a team went to the island to identify where Mr Chau was killed.
They said the investigation is ongoing and a committee has been formed to find out the details and review the mechanisms in place to prevent unauthorised entry to the island to prevent any similar further incidents.