'The aerial sighting of the bodies in the sand by our helicopter clearly contradicts the popular belief that the Sentinelese are cannibals,' said Deputy Commandant Pankaj Verma of the Indian Coast Guard.

Marco Polo, who sailed through the archipelago in 1290 while transporting a Chinese bride for an Indian prince, claimed that the aborigines inhabiting the Andamans 'are no better than wild beasts ... and eat everybody that they can catch, if not of their own race'.

The indigenous people of the Andamans are often labelled 'Stone Age' or 'primitive', despite protests from tribal rights organisation Survival International that such descriptions directly result in their persecution.

The previous time the forest-dwelling Sentinel Islanders are known to have killed anyone was in 1896. That was when the corpse of an escapee from the British, who first colonised the islands, was found on a beach 'pierced in several places with arrows, and with its throat cut'.

'In my experience of 30 years, I've seen that the Sentinelese are not wanton killers - they never attack without warning,' said Andamans environmentalist Samir Acharya. 'The fishermen who were killed last month had criminal records, including murder, and were illegally hunting for lobster and mud crab within the sacrosanct three nautical mile restricted zone around the island.'

The Sentinelese are one of four Negrito tribes, acknowledged as 'the last of the first humans', living in the Andamans, and the only ones who continue to ferociously rebuff any contact with the outside world.

They are found only on a small, heavily forested island called North Sentinel, barely 7km west of the archipelago's main island. Survival International estimates their numbers to be between 50 and 200.

In order to protect the pre-historic Sentinelese way of life and keep the island free of modern diseases, the Indian government has banned all visitors from North Sentinel, including officials and even anthropologists.

But there has been concern for the fate of the Sentinelese since the tsunami hit the Andamans in December 2004.

'The tsunami altered the topography of North Sentinel, hampering the ability of the tribes people to fish,' said anthropologist Anstice Justin, who surveyed the area immediately after the natural disaster. 'The island got tilted, the coral reef was exposed on one side, and a lagoon disappeared.'

The sea is an important source of food for the Sentinelese. But since they have not invented oars, they can fish only in shallow waters, propelling their outrigger canoes with poles. The lush, pristine island also has wild pigs and birds, besides fruit and coconut trees planted by Dr Justin in 1986.

'We've been anxious about the condition of the Sentinelese, but there is no way we can visit the island now,' said the anthropologist.

But after the dramatic incident last month, experts seem a little less worried about the fate of the islanders.

'The way the Sentinelese reacted suggests they are in pretty good health and not short of resources,' said Mr Acharya.

Displaying typical defiance of the modern world, the tall, wiry tribes people tried to shoot their primitive arrows at the Coast Guard helicopter sent to locate the two missing fishermen, while some others cavorted like children in the motorised fishing boat they had seized.

In the past, they have fired arrows not just against approaching motor boats but also against an Indian Navy warship. Once an arrow even pierced the windshield of a low-flying Coast Guard helicopter, barely missing the pilot.

'Unfortunately, we know very little about the Sentinelese, and have had no dialogue with them,' said Dr Justin, one of the few to have actually visited an encampment, abandoned at that time, on North Sentinel in 1992.

'All we know is that they are hunter-gatherers who use fire and have somehow discovered iron, which they fashion into arrow heads and harpoons,' he added. 'They sleep in communal huts around hearths, and appear to move camp several times during a lifetime.'

Shipwrecks have been the main source of iron for the Sentinelese, the last time in the 1980s. At that time, Indian salvage companies had also sent workers to the island to retrieve the metal from two stranded ships.

'Just what interaction they [the workers] had with the natives ... is obscure,' said Madhusree Mukherjee in her seminal book The Land of Naked People - Encounters with Stone Age Islanders. 'Some said they gave coconuts to the Sentinelese; others claimed to have shot them indiscriminately.'

Inexplicably though, the Sentinelese became less hostile after this encounter, leading to an historic moment in January 1991 when an islander came up to a boat and accepted a gift. But they soon turned hostile again.

As a result, the Sentinel Islanders remain the world's most mysterious people. They have never been studied by anthropologists, and nobody, not even other Negrito tribes in the Andamans, can understand their language.

'The whole idea has been not to disturb their way of life,' said DS Negi, chief administrator of the Andamans. 'But we really have to consult anthropologists and other social scientists on the question of whether these Stone Age aborigines should be studied.'

Though anthropologists are keen to explore the culture of the Sentinel Islanders, Survival International's director Stephen Corry warned that 'contact with the outside world could very quickly wipe out this unique and vulnerable tribe. The local administration must ensure that the Sentinelese are left alone as long as that is their wish - and what happened last month made it very clear that it is.'

History seems to justify a hands-off policy. Ever since the Andamans was colonised by the British around 150 years ago, the three other Negrito tribes - the Great Andamanese, the Jarawa and the Onge - have been devastated, first by war and then by disease or modern addictions such as tobacco and alcohol.

'The Jarawas came into contact with us less than 10 years ago, and already half of them have hepatitis B, while many have been afflicted with measles, viral fevers and skin diseases,' said Mr Acharya, who set up Sane, the Society for Andaman and Nicobar Ecology.

'Until we discover how to prevent the consequences of our intervention, let us at least leave the Sentinel Islanders alone.'