Indian authorities said on Friday they are investigating whether a young American believed to have been killed by an isolated tribe on a remote island, may have had help from more people than initially thought to make his illegal voyage.

John chau

Port Blair:

John Chau, 26, was allegedly killed on Nov. 17 by people of the Sentinelese tribe who inhabit the North Sentinel Island in the Andaman and Nicobar island chain. Chau’s family said in a social media post he was a Christian missionary and mountaineer.

It is illegal for people to visit the island and seven people suspected of helping Chau reach it, including fishermen, have been arrested.

The fishermen told police that they saw Chau’s body being dragged across a beach and buried in the sand.

Police are now investigating if Chau had help from other people to travel to North Sentinel, Vijay Singh, senior superintendent of police (SSP) in the Andaman and Nicobar islands, said in a statement.

Police would investigate “the sequence of events, the sea route followed”, and other matters, said Singh.

The Sentinelese, hunter-gatherers armed with primitive spears and bows and arrows, are considered to be the last pre-Neolithic tribe in the world and the most isolated such group.

The tribe, estimated to be only a few dozen in number, have for decades aggressively resisted contact with the outside world.

Anthropologists were briefly in contact with the tribe in the early 1990s, but their effort was abandoned due to fears that contact with the outside world could expose the tribe to pathogens and lead to their extinction.

North Sentinel, 50 km (31 miles) west of Port Blair - the capital of the island cluster - is protected by laws which bar even fishing within a 5-nautical mile radius of the island. The law also bars tourism or photography. Those guilty of breaking the law face jail of up to three years.

In a social media post, Chau’s family called on authorities to release his friends in the Andaman Islands saying they did not blame anyone for his death.

Dependra Pathak, director general of police in the Andaman and Nicobar islands, told Reuters police had to follow the law.