The arrival of 13 unmanned bamboo rafts on the island of Yap in the Federated States of Micronesia has locals both puzzled and afraid - especially as some carried human remains. 'In 30 years of covering the Pacific, I've found it's always the mysterious stories of the sea that evoke the greatest interest and the greatest fear,' said Michael Field, a New Zealand-based journalist who broke the story last week. 'The people of Micronesia are utterly terrified by these arrivals. There's something primordial about it. They have an intense and close relationship with the sea and here are these ghosts arriving from the sea. It's very freaky,' he told the South China Morning Post. The rafts, made of bamboo not found in the Pacific, started arriving late last year. The last two carried a few skulls and skeletons, including that of a child. One skull had a hole in the forehead, which Micronesian police say is too small to be a bullet hole. Initial speculation as to the rafts' origins points to Indonesia. A faded identity card, issued in the northern Sulawesi port city of Bitung 1,700km away, was found on one of the rafts. An Indonesian diplomat is said to be heading to Micronesia to pursue the matter. But the Ministry of Foreign Affairs in Jakarta denied all knowledge of the mystery and of the diplomat. A ministry spokesman said on Friday that he had checked with his colleagues in Manila and Canberra, but they too knew nothing of the mystery. Some islanders say the victims may have been refugees fleeing sectarian conflict in Maluku. This theory brings to mind the alleged massacre by Indonesian troops of separatists in Papua (formerly Irian Jaya) in 1998, when scores of bodies were allegedly thrown into the sea off the island of Biak. Officials claimed the corpses were actually victims of the tsunami that struck the Papua New Guinea coast 900km away. Rights activists have never been convinced of this. There is no doubt that many people believe a tragedy lies behind the arrivals. But if it was a massacre, why would the perpetrators build rafts for their victims? Another theory is that the rafts could have been launched during a funeral ritual. But this seems unlikely due to the rarity of the bamboo used. The islanders also think the victims could have been part of the vast and profitable people-smuggling trade that operates in Southeast Asian waters. Many people are also mystified at why only two rafts arrived with human remains. It is likely that bodies could have been swept off the rafts in high seas, but how is it then possible that some remains managed to stay on board? Were the people tied to the rafts in some cases and not in others? And if the hole in the skull was not from a bullet, what caused it? The most likely scenario - and the one many Pacific experts believe - is that something tragic happened to a community. Something that prompted an organised departure. Finding out the truth, however, is bound to keep investigators busy for many months.