Mystery of Skeleton Lake solved: Scientists reveal bones found around edges of Indian lake belonged to hundreds of 9th century tribesmen who died in freak hail storm More than 200 skeletons discovered by British patrol during World War II Bodies thought to be Japanese soldiers actually dated back to 850AD Now expedition confirms blows to head which killed group were hailstones Scientists believe they have finally solved the mystery of how the skeletons of more than 200 people came to be in a frozen lake in northern India. The skeletons, which were first discovered by a British forest guard in 1942, were initially thought to be the bodies of Japanese soldiers travelling through India as part of a World War II land invasion. But although the cold climate around the Lake of Roopkund, at 16,000ft above sea level, had preserved some of the hair, flesh and leather clothes of the victims, the bodies were dated to around 850AD. The mystery of how dozens of skeletons ended up on the shores of the Lake of Roopkund has puzzled locals and scientists for centuries Scientists discovered they appeared to be from two main groups - one was closely related which seemed to be a family group and another of shorter local people. They concluded that the family were likely to be pilgrims heading through the valley with the help of the locals as guides. Theories ranging from a landslide to a mass suicide were put forward to explain the deaths, but it is only now that researchers believe they know what caused the cracks in their skulls. During World War II the British government feared they were the remains of Japanese soldiers, but tested showed they were much older Now scientists believe a sudden freak hailstorm is to blame for the cracked skulls of the dead The skeletons remain littered around the lake's edge The Lake of Roopkund is in northern India near Nepal A 2004 expedition to the site concluded the group was killed by cricket ball-sized hailstones during a sudden storm. This, they decided, was the only way to explain why the skulls and shoulder bones of the dead had all been hit by rounded objects directly from above. As there was nowhere to shelter in the valley, the group was at the mercy of the storm. Their bodies lay in the lake, which regularly freezes, for the next 1,200 years until their wartime discovery. More: The Skeleton Lake of Roopkund, India