Covid-19 pandemic and challenged those claiming to know better to come forward with the smoking gun.A WHO investigative team is in Wuhan, China -- where the first cases were discovered in December 2019 -- trying to piece together how the virus jumped from animals to humans before going on to kill more than two million people.Also Read | How India can fight vaccine hesitancyThe UN agency's emergencies director Michael Ryan hit out at those sniping at the mission, and said people claiming they have information on how the pandemic broke out should emerge from the shadows.Ryan said many critics were saying they "won't accept the report when it comes out", or that there is "other intelligence available that may show different findings" on how.