Transcript for Science, intelligence communities look into the origins of COVID-19: Part 1
You were talking about a bioengineered monster virus, and you were ruling that possibility out? We were ruling that possibility out. I definitely have a great respect for nature. But we also have to have a great appreciation for what humans can do. No one knows that. It's a scientific question that has ignited a political firestorm, now with renewed attention as the possibility of an accidental lab leak gains prominence. President Biden has even asked intelligence agencies to redouble their efforts to investigate the origins of covid-19, and multiple probes have been launched around the world, including one led by the U.S. State department and another by the world health organization. We need to know the origin of this virus. All determined to uncover the truth. Could this novel coronavirus come from the dark side of mother nature or from a lab? And if it did come from a lab, was it an accident or could it have been an engineered bioweapon? That deadly coronavirus now grows, spreading from Wuhan, China. A city of 11 million people, home to several large wildlife markets, potential breeding grounds for viruses. But Wuhan is also home to one of the leading laboratories in the world studying bat coronaviruses. And from early on, that had people wondering. There is a famous quote in the movie "Casablanca." Of all the gin joints in all - the towns of the world, she walks into mine. So of all the places in the world where there could be a natural outbreak in the wild, what are the chances that that would not just happen in Wuhan with the world's largest - collection of bat coronaviruses? This is such a political topic. It's so charged. It's a giant puzzle. And like, you know, 95% of the pieces are missing. Reporter: The evidence we do have is both circumstantial and scientific. The bustling city of Wuhan remote caves in southern China thousands of miles away to the genetic structure of the virus itself. And complicating the task of solving this mystery, the whole topic has become weaponized, a political cudgel. They could have stopped it, but they allowed it to come out. China virus. Kung flu. With some like David asher who ran the state department's investigation into the origins of the covid virus accusing China of negligence for not alerting the world sooner. We're talking lights out. There was no cooperation. And there is still no Reporter: So let's begin with an undisputed scientific fact. Viruses are constantly emerging from nature. So when you look at this virus with your expertise, you see the workings of evolution and of nature. You don't see the hand of some diabolical scientist cooking up Absolutely that just didn't happen at all. Reporter: Robert Gary of tulane university is one of the world's leading virologists. Look at the data a little closely. I think that most scientists and certainly most virologists have already done this will come to the conclusion that we're looking at a virus that comes from nature. Reporter: Gary argued the genetic code of the virus looks like the kind of thing that happens randomly in nature, not in lab. It's really nothing that any experienced virologist or even your worst graduate student would do. Reporter: And that remains the consensus among most virologists, that this coronavirus has none of the telltale fingerprints of overt bioengineering. So if this had been cooked up in a lab, you'd be able to see that? Yes. And we don't see that? No. Dennis Carroll runs the global virome project, a project to identify virus's in the wild that have the potential to trigger future pandemics. Carroll and many other virologists say every option should be explored. But there is another likely origin story, wet markets. Large open stall markets where live animals are sold. In the wet market, you would find a menagerie of different wild and domestic animals all mixed together, and people will go in and purchase. Those conditions are very, very amenable to spillor events. Reporter: It's fall 2019. The house speaker Nancy Pelosi has decided to open a formal impeachment -- Reporter: An impeachment inquiry has just been announced. Hurricane Dorian, growing over the past 24 hours -- Reporter: As a hurricane brews in the atlantic. But something else may have been brewing in Wuhan. These satellite photos seen here for the first time show various Wuhan hospitals, evidence suggesting the virus was spreading. Then in January 2020, all eyes turned to that live animal market in Wuhan. But a stubborn puzzling fact emerged. Of the first several dozen cases of covid in Wuhan, almost half of them cannot be traced back to that wet market. And the director of the Chinese CDC, GAO Fu later revealed that none of the animal samples taken from the market tested positive for the virus either. Adding at the beginning we presumed that the seafood market may have the novel coronavirus, but now it turns out that the market is one of the victims. They had hoped that they would find the host animal at that market, and that's not what they found. What we know now is that the virus was likely spreading in the city before it was detected. The wet market was actually the accelerating agent for the virus and not the initial spark. The search for the virus' origin continued. Investigators, including some inside the U.S. Intelligence community started focusing on a building a few miles from the wet market, the Wuhan institute of virology. Jamie metzl is a member of the world health organization's expert committee on human genome editing, and like many others, he has long been concerned about the research that was taking place at the Wuhan institute. They were doing what some people have called gain of function research, seeing how the world's scariest viruses might infect human cells. Do you think they were playing with fire? Absolutely I do. But there were lots of virologists who were in on this. And the idea was let's understand these viruses so we know what we're facing. The counterargument was we're plaing with fire. If it turns out that covid-19 stems from an accidental lab incident from the Wuhan institute of virology, it will turn out that that fear was certainly well-founded. The Wuhan institute is one of China's few level 4 labs with the highest level of biosecurity, enabling them to deal with the world's deadliest pathogens. It's famous in the scientific community, and so is its star researcher Dr. Shi zhengli, dubbed the bat woman for her work collecting and studying viruses from bats. She said that none of the sequences of the viruses that she collected matches the covid pandemic virus. Yes. Doesn't that clear the lab? If you believe that one, she has all the information, and two, she is telling the truth. Dr. Shi admitted early in the pandemic that she was worried the virus could have leaked from her lab. She told an American science journal that she remembers thinking oh, my gosh, if this is a bat coronavirus, could my lab and the samples I've been working with be involved? When Shi zhengli learned that none of the samples that had been collected of this new virus in the earliest cases of coronavirus didn't match any of the samples that she and her team had sequenced from bat caves in years prior, she breathed a sigh of relief. The Wuhan lab had been collecting potentially deadly viruses for years, some from an aandoned copper mine in southwestern China. In 2012, there were these six Chinese miners who were sent down into a mine in southern China to clean out the Batman newer. They all got infected with what now looks like covid covid-19-like systems. Three of them died. Researchers collected viruses where similar coronaviruses have been found. One of those coronavirus samples was 96% similar to the virus that has caused this pandemic. Politicians and nonscientifics have speculated that it's possible that virus was brought back into a lab and somehow transformed to become our current coronavirus, but what virologists say is that that's simply not the case. There is no virus that's close enough that you could use any type of research to get to sars-cov-2. You could hypothesize I suppose that the investigators at the Wuhan institute of virology had some virus that was closer and they just weren't telling us about that. Do you believe that this virus spent any time in a laboratory? Before the pandemic, absolutely not. When we come back, what happened when bbc reporters tried to go to that cave, and what Dr. Shi said at an American college about covid-19 leaking from her lab.
This transcript has been automatically generated and may not be 100% accurate.