New evidence has emerged about the alleged role of United Nations troops in causing a cholera epidemic in the Caribbean nation of Haiti.
A top US cholera specialist, Dr Daniele Lantagne, said after studying new scientific data that it is now "most likely" the source of the outbreak was a camp for recently-arrived UN soldiers from Nepal - a country where cholera is widespread.
Dr Lantagne was employed by the UN itself in 2011 as one of the world's pre-eminent experts on the disease.
The new evidence could have serious implications for the UN, which is facing an unprecedented legal and moral challenge in Haiti - as well as a multi-billion dollar compensation claim from victims' families.
More than 7,500 people have died from the cholera epidemic in Haiti since it started in late 2010. Hundreds of new cases are still being registered every week.
It is by far the largest cholera outbreak in the world in recent years - with more cases than on the whole of the African continent.
Prior to this outbreak, and despite Haiti's many other problems - including a devastating earthquake in January 2010 - the country had not recorded a single case of cholera for over a century.
Cholera is spread through infected faeces and once it enters the water supply it is difficult to stop - especially in a country like Haiti which has almost no effective sewage disposal systems.
After studying molecular data known as full genome sequencing on the strain of cholera found in Haiti - and that prevalent in Nepal in 2010 - Dr Lantagne said: "We now know that the strain of cholera in Haiti is an exact match for the strain of cholera in Nepal."