The World Health Organisation (WHO) came to Wuhan with four theories about the origins of COVID-19.
They will leave China with three.
The four ideas were that it jumped directly from animals to humans, that it spread via an intermediate host, that it was imported in from somewhere else, or that it came from a laboratory.
Out of those, only the lab leak has now been discounted as "extremely unlikely". Further research into it will not be pursued - at least not by them.
It has always been a contentious idea - one put forward by the administration of Donald Trump without much evidence, and dismissed by others as a conspiracy theory.
But there was scientific merit in examining it.
As one of the WHO investigators, Peter Ben Embarek, told me - accidents do happen and there are a number of virus laboratories in Wuhan. The WHO team had said they were not ruling it out.
After four weeks in China, though, the WHO have dismissed it - all 17 experts voted unanimously, according to another team member.
That's after visiting the Wuhan Institute of Virology and speaking with scientists there.
Sceptics will pour over the full WHO report explaining their reasoning.
As for the other three theories, we are not much closer to understanding where COVID came from.
Peter Ben Embarek said its transmission and circulation could have followed a long, convoluted path. And so too will the research.