Indian police trying to recover the remains of an American missionary killed by an isolated tribe are consulting anthropologists and staking out the island where he was attacked.

Officers in the Andaman and Nicobar Islands, a remote Indian territory, are trying to determine whether the body of John Allen Chau can be retrieved, and whether any tribespeople can be charged for killing him after he trespassed on North Sentinel Island on 16 November.

Police believe Chau, 26, a self-styled adventurer from Washington state, was killed nine days ago on the forested island about two-thirds the size of Manhattan in the Bay of Bengal.

His death at the hands of the one of the world’s most mysterious communities has thrown up two new questions: Can Chau’s remains be recovered? And can anyone be prosecuted for killing him?

“It is certainly the most unique case in my career,” said Dependra Pathak, who left his post overseeing traffic policing in the Indian capital Delhi five months ago to become the director general of law enforcement in the Andamans.

Police have attempted one aerial survey and two by boat since Chau’s death was first reported to officers on Tuesday. A helicopter flew over the island on Wednesday but kept its distance: the Sentinelese, an isolated tribe at least 30,000 years old, have shot arrows at helicopters that have approached too closely in the past.

On Friday, police sailed to within about 300 metres of the island, bringing one of the fishermen alleged to have assisted Chau to reach the shore, and who says he saw his body being buried there on 17 November.

“We located the place of this incidence and got a sketch map – this is a mandatory requirement in a criminal investigation,” Pathak said. “For about three hours we watched, and in this time we saw five or six Sentinelese moving about on the beach.

“They were carrying a bow and arrow and looking towards sea side. I would say they were very watchful.”

Police are interviewing anthropologists who have studied or interacted with the tribe, loosely estimated to number 100 people, for clues on how they respond in the aftermath of death.

“Because they have killed somebody from outside, they have to have suffered a psychological shock,” he said. “Understanding this will help us in observing them and to draw a strategy if we want to move forward.”

When a boat ran aground on North Sentinel Island in 2006, the two fishermen onboard were killed and buried in the sand. After about a week, according to police records, the tribespeople dug up the pair and hung them from bamboo poles facing the ocean.

Should the Sentinelese do the same with Chau, it could present the only opportunity to identify or retrieve his body.

“As per our information in that [2006] case, after five to seven days they had taken the body out of the sand and made it stand with the help of bamboo, facing the sea,” said Pathak.

A criminal case has been registered against “unknown tribesmen”, in line with mandatory police procedures, but Pathak said it was unclear if police could even lawfully land on the island to arrest someone. “As per law, no one can go there, not even police,” he said.

“There is a responsibility and obligation on us to handle the case with great sensitivity because there is a small group, in a small place, and they have their own civilisation and world view. We have no plans to barge in and have a confrontation,” he said.

Kanchan Mukhopadhyay, a researcher with the Anthropological Survey of India who was previously stationed in the Andamans, said trying to retrieve Chau’s body threw up too many problems to be realistic.

“It’s a restricted area and the government has decided a hands-off policy,” he said. “One has to go there, land there – and if they resist, what are we going to do?”

He said Chau, who wrote that he wanted to “declare Jesus” to the Sentinelese, had knowingly violated the will of the tribe. “And this retrieval of the body will again violate the will of the people.”

Seven people including five fishermen have been arrested for helping Chau reach close to the island – which he had labelled “Satan’s last stronghold” in his diary – on the evening of 14 September. According to his journal entries, he managed to set foot on the shore the following day, but was chased back on to the boat by the Sentinelese.

He wrote that night: “I don’t want to die. Would it be wiser to leave and let someone else continue? No. I don’t think so. I still could make it back to the US somehow, as it almost seems like certain death to stay here.”

The next afternoon, he kayaked back to the island. Two fishermen saw the Sentinelese dragging his body and burying it the next morning.

The Sentinelese are regarded as one of the world’s most isolated communities, resisting both British colonisers and efforts by Indian administrators to integrate them into the surrounding islands. Since 1996 the Indian government has had a policy of leaving the tribe alone, enforcing a buffer zone around their island.