By Kathryn Westcott
When two unrelated human feet washed up on the beaches of two small islands north of Vancouver in six days last August, a police spokesman said the odds of it happening were a million to one. This week the number of feet found rose to five.
What's going on? Police in British Columbia are confounded, saying they have never seen a case like it.
The feet have all been recovered along the shorelines of the Strait of Georgia, which lies to the south and west of Vancouver.
They were all encased in trainers, and most are right feet. Police say they have found no evidence of the feet being severed and that it is not clear whether a crime has been committed.
DNA has been collected from some of them, but police say that there has been no match to anyone on their missing persons database.
The unusual nature of the case has prompted much amateur speculation about murder mysteries, links to organised crime or to the 2004 Asian tsunami.
Experts initially speculated that the feet could have drifted more than 1,500 miles.
However, as the number has risen, estimates of the distance travelled have fallen.
Curtis Ebbesmeyer, a Seattle-based oceanographer who specialises in how things float on the ocean's currents has dismissed any connection with the Asian tsunami, on the grounds that the distance is just too vast.
He has suggested that the feet could be a result of a possible accident along the Fraser River, which washed down and spread out along the Strait of Georgia.
Dr Simon Boxall, an oceanographer from the National Oceanography Centre in Southampton in the UK, agrees that the feet are unlikely to have travelled far.
"The fact that they are being found repeatedly along the same stretch means they have to have come from roughly the same source, and that source is likely to be local," he told the BBC News website.
He added that because of the way objects are dispersed by ocean currents, the odds are very low of five feet that originated hundreds of miles away ending up in one relatively small area.
Experts say trainers could have preserved the feet
If, for example, they had travelled from as far away as Hawaii, there would have to have been thousands in the first place for so many to turn up in one area, he said.
In his view, it's a coincidence that most of the feet are right feet, as there is no reason why right and left feet should float in different ways.
And why is it that just feet have been found?
Mr Ebbesmeyer was quoted in the Vancouver Sun as saying that when bodies decompose, they break into 10 pieces, two arms, two legs, two feet, two hands, the head and the torso.
Experts say that it's the running shoes that explain why only the feet are turning up.
They would have helped keep the decomposing feet intact, and protect them from fish. The soles would also have helped them float, allowing them to be swept away from the rest of the body.
Police have said it is possible the feet come from the passengers aboard a small plane which crashed into the water in the region several years ago - their bodies were never recovered.
The Coroners Service of British Columbia has investigated this idea but to date, it has failed to match DNA samples collected from members of the crash victims' families with DNA obtained from some of the mystery feet.
Dr Joseph Finley, a physical scientist and retired special agent with the FBI, told Canada's National Post newspaper that depending on the race of the victims, the feet might belong to stowaways who hid on commercial ships heading for Alaska.
Dr Boxall acknowledges that forensic scientists working to recover DNA profiles from feet could have an extremely difficult task on their hands.
Even if the remains are identified, scientists may not be able to determine how and when the victims died.
"Seawater can be horrendous," he says. "It can corrode very quickly or, bizarrely, it can preserve things quite well - it depends on how much biological activity there is at the time."
Dr Gail Anderson, a specialist in decomposition at the Simon Fraser University was quoted in the New Scientist as saying that we "know next to nothing about what happens to bodies under water" but she added that feet normally come apart from legs.
Flesh immersed in water turns into adipocere tissue, she says, a soap-like substance, that no microbes or scavengers such as crabs will eat.
It is likely the case will remain a mystery for some time. As one investigator put it this week, this is not CSI - a reference to popular fictional TV show in which challenging forensic cases are solved in no time.