bats. >> they sampled case of from all over southern china. in some cases they had to crawl on their bellies to get in through the tight crevices into the caverns were bats are. they collected lots of bat samples, then took all these samples back to the lab. >> it would take almost a decade. remember that, nearly ten years, to figure this out. but dr. lee's work confirmed that sars i had in fact started in bats. now, by the time covid was first detected in 2019, the wuhan institute of virology was home to the largest collection of bat coronavirus samples in the world. >> she also worried because her lab's in wuhan. is there a chance it could have come from our lab? >> within days, her team had isolated the virus, sequenced it, then shared its full genome. >> as soon as they had the sequence, they were able to determine it had never been in her lab, had nothing to do with the viruses she had studied