NEW DELHI, Nov. 27 (Xinhua) -- The police in India's Andaman and Nicobar islands, located in the Bay of Bengal, have failed to recover the dead body of the U.S. citizen who was killed by isolated tribals - "Sentinelese" on Nov. 16, after seeing the tribesmen armed with spears, bows and arrows.

The police say that they are not authorized to force their way into the tribesmen's territory, as "they are a treasure".

"They are a treasure. We cannot go and force our way in. We don't want to harm them," said Andaman and Nicobar islands' top police officer Dependera Pathak.

"We watched them from a distance and they watched us from a distance. We are looking carefully at what happened then, and what the Sentinelese did. We are consulting anthropologists to see what kind of friendly gesture we can make."

The police have tried to approach the island inhabited by the tribals, who, it is believed, are descendants of Africans and migrated to the area about 50,000 years ago. They survive on the small, forested island by hunting, fishing and gathering wild plants. Almost nothing is known of their lives, except that they attack outsiders with spears or bows and arrows, reported the English daily Hindustan Times.

According to media reports, U.S. citizen John Allen Chau had intruded into the Sentinelese' island on Nov. 16 after allegedly bribing the local fishermen, in a bid to interact with the tribesmen. As per the Indian laws, entering the isolated island is strictly prohibited.

The fishermen, who have been in police custody ever since the incident happened, told the local government authorities that they saw the Sentinelese killing and burying Chau's body on the beach. The notes Chau left behind reportedly say that he wanted to convert the islanders to Christianity.