What's to investigate?
The Wuhan Flu either came from the disgusting practice of the Chinese to mix all its weird food animals together in one combination slaugherhouse-restaurant, a theory that's largely rejected now, or it came from the release, planned or otherwise, of a half-assed SARS the ChiComs were experimenting with using all the safety practices of a squad of fourth graders.
Then there were the known deliberate efforts of Winnie the Pooh to spread the infection globally.
WHO has as much credibility now as the UN Human Rights Commission.