According to Chinese studies, they believed the virus is not man-made, but by doing Y-DNA studies about the virus, they suggest the original of the virus is likely traced back to the US in 2019.
The theory is the virus was around in US for a while, remain unknown in the US for a while (e.g. mistaken for flu or other causes), then transmitted to Wuhan during the 2019 world military Olympic games hold there.
The main proof of this theory is, by study Y-DNA of the virus, it can be found that the virus in China can only traced back to 2 common ancestors, whilst for the cases in the US, they have all 5 common ancestors (Y-DNA) of the virus.
The side-proof about this theory is:
(1) There are lots of flu-death caused by unknow-virus reported in 2019 in the US
(2) The residency of the US team in 2019 military Olympics games is only a street away from the Wuhan Huanan wet-market.
(3) Only about 1-2 months later after the games, the first case of Wuhan virus patient identified, as for the delay, it is perfect reasonable since such virus become more infective and deadly when winter comes.