London - It was an archaeological hoax that fooled scientists for decades. A century on, researchers are determined to find out who was responsible for Piltdown Man, the missing link that never was.In December 1912, it was announced that a lawyer and amateur archaeologist named Charles Dawson had made an astonishing discovery in a gravel pit in southern England - prehistoric remains, up to one million years old, that combined the skull of a human and the jaw of an ape.Piltdown Man - named for the village where the remains were found - set the scientific world ablaze. It was hailed as the missing evolutionary link between apes and humans, and proof that humans' enlarged brains had evolved earlier than had been supposed.It was 40 years before the find was definitively exposed as a hoax, and speculation about who did it rages to this day. Now scientists at London's Natural History Museum - whose predecessors trumpeted the Piltdown find and may be suspects in the fraud - are marking the 100th anniversary with a new push to settle the argument for good.The goal, lead scientist Chris Stringer wrote in a comment piece published on Wednesday in the journal Nature, is to find out "who did it and what drove them" - whether scientific ambition, humour or malice.DoubtsStringer heads a team of 15 researchers - including experts in ancient DNA, radiocarbon dating and isotope studies - examining the remains with the latest techniques and equipment and combing the museum's archives for overlooked evidence about the evidence unearthed at sites around Piltdown."Although Charles Dawson is the prime suspect, it's a complex story," said Stringer, the museum's research leader in human origins. "The amount of material planted at two different sites makes some people - and that includes me - wonder whether there were at least two people involved."Doubts grew about Piltdown Man's authenticity in the years after 1912, as more remains were found around the world that contradicted its evidence. In 1953, scientists from London's Natural History Museum and Oxford University conducted tests that showed the find was a cleverly assembled fake, combining a human skull a few hundred years old with the jaw of an orang-utan, stained to make it look ancient.Ever since, speculation had swirled about possible perpetrators. Many people think the evidence points to Dawson, who died in 1916.Other long-dead suspects identified by researchers include Arthur Smith Woodward, the museum's keeper of geology, who championed Dawson's discoveries and gave them vital scientific credibility. The finger has also been pointed at museum zoologist Martin Hinton; Jesuit priest and palaeontologist Pierre Teilhard de Chardin; and even Sherlock Holmes author Arthur Conan Doyle, who lived near Piltdown.Stringer said the key may lie in a later find nearby - a slab of elephant bone nicknamed the "cricket bat" - that seemed to back up the first Piltdown discovery. It was revealed as a clumsy fake, carved with a steel knife from a fossilised elephant femur.HoaxOne theory is that Hinton - sceptical but afraid to openly question Woodward, his boss at the museum - might have planted it thinking it would be spotted as a hoax and discredit the whole find. A trunk with Hinton's initials found in a loft at the museum a decade after his death in 1961 contained animal bones stained the same way as the Piltdown fossils.Miles Russell, senior lecturer in archaeology at Bournemouth University, thinks the museum's work may shed new light on how the forgery was done. But he thinks there is little doubt Dawson was the perpetrator."He is the only person who is always on site every time a find is made," Russell said. "And when he died in 1916, Piltdown Man died with him."Russell is author of the new book The Piltdown Man Hoax: Case Closed - though he doubts speculation about the century-old fraud will stop."People love conspiracy theories," he said. "And this is one of the biggest scientific hoaxes of all time."Whoever was behind it, the hoax delayed consensus on human origins, leading some scientists to question the authenticity of later finds because they did not fit with Piltdown Man.Stringer said Piltdown Man stands as a warning to scientists always to be on their guard - especially when evidence seems to back up their theories."There was a huge gap in evidence and Piltdown at the time neatly filled that gap," he said. "It was what people expected to be found. In a sense you could say it was manufactured to fit the scientific agenda."That lesson of Piltdown is always worth learning - when something seems too good to be true, maybe it is."