Naturalists reported the first mass toad murder in 1997 when hundreds of legless corpses were found in south-west Scotland. Scientists who examined the bodies said the legs had been expertly removed by pulling them out of their skin, leaving it turned inside out like a pair of used stockings.
Suspicion fell on local restaurateurs who had perhaps decided to experiment with an alternative ingredient for exotic French dishes - but a new analysis suggests they are in the clear. Now the finger of suspicion has fallen on the otter.
Paul Duff, a vet in Culgath, Cumbria, and Stephen Hewitt, curator of natural sciences at Tullie House Museum in Carlisle, reopened the files of two similar incidents last year.
At Winterhope reservoir, in Dumfries and Galloway, 355mutilated toads were counted near the water's edge; while more than 30 toads were slaughtered in a pond in a private garden.
Pathology tests found that all the animals had suffered the same fate - a neat incision along the belly followed by the removal of the legs by pulling or "degloving" them.
"There were, however, a number of significant additional findings," the two researchers report in Veterinary Record.
When they re-examined the dead toads they found that some had suffered puncture holes in their skin - probably caused by tiny teeth. The remnants of toad leg bones were then found in nearby "spraints" or dung deposits of the British otter, Lutra lutra.
"There are now several reasons for considering that these incidents were caused by free-living predators rather than humans," say the pair. "The reservoir is an open area without cover, and humans might be expected to ... remove the toads and then dismember them in a more private location."
Mr Hewitt said that although the evidence falls short of proof that otters were to blame, it is the most incriminating information yet to emerge.
But one mystery remains. "It is curious that we have had no previous reports of large numbers of toads being killed in this way," Mr Hewitt said. He suggested that one or two otters may have learnt to extract the fleshiest parts of the toad - the legs - from the foul-tasting skin.
The recovery of the local otter population could also make such mass killings more obvious than in previous years.