What we found as part of this WHO mission to China is that there is a pathway. The theory is that somehow that virus got from a bat into one of these wildlife farms. And then the animals were shipped into the market. And they contaminated people while they were handling them, chopping them up, killing them, whatever you do before you cook an animal. They're a traditional food. Civets, these are like ferrets. There's also an animal called a ferret badger. Rabbits, which we know can carry the virus. Those animals were coming into the market from farms over 1,000 miles away.

Lesley Stahl: Were you able to test any of the animals found in the Wuhan market for the virus?

Peter Daszak: Well, the China team had done that, and they found a few animals left in freezers. They tested them, they were negative. But the fact that those animals are there is the clue.

Lesley Stahl: But there's no direct evidence that any of those animals were actually infected with the bat virus?

Peter Daszak: Correct. Now what we've gotta do is go to those farms and investigate. Talk to the farmers. Talk to their relatives. Test them. See if there were spikes in virus there first.

Lesley Stahl: So, the team doesn't actually know if any of the farmers or the truckers were ever infected?

Peter Daszak: No one knows yet. No one's been there. No one's asked them. No one's tested them. That's to be done.

Something like 75% of emerging diseases come from animals into people. We've seen it before. We've seen it in China with SARS.

Peter Daszak: For an accidental leak that-- that then led to COVID to happen, the virus that causes COVID would need to be in the lab. They never had any evidence of a virus like COVID in the lab.

They never had the COVID-19 virus-- Not prior--to the outbreak, no. Absolutely. No evidence of that. : I'm on the WHO team for a reason. And, you know, if you're going to work in China on coronaviruses and try and understand their origins, you should involve the people who know the most about that. And for better or for worse, I do.

Peter Daszak: We met with them. We said, "Do you audit the lab?" And they said, "Annually." "Did it you audit it after the outbreak?" "Yes." "Was anything found?" "No." "Do you test your staff?" "Yes." No one was--

Lesley Stahl: But you're just taking their word for it.

Peter Daszak: Well, what else can we do? There's a limit to what you can do and we went right up to that limit. We asked them tough questions. They weren't vetted in advance. And the answers they gave, we found to be believable-- correct and convincing.

Lesley Stahl: But weren't the Chinese engaged in a cover-up? They destroyed evidence, they punished scientists who were trying to give evidence on this very question of the origin.

Peter Daszak: Well, that wasn't our task to find out if China had covered up the origin issue.

Lesley Stahl: No, I know. I'm just saying doesn't that make you wonder?

Peter Daszak: We didn't see any evidence of any false reporting or cover-up in the work that we did in China.

Lesley Stahl: Were there Chinese government minders in the room every time you were asking questions?

Peter Daszak: There were Ministry of Foreign Affairs staff in the room throughout our stay. Absolutely. They were there to make sure everything went smoothly from the China side.

Lesley Stahl: Or to make sure they weren't telling you the whole truth and nothing but the truth--

Peter Daszak: You sit in a room with people who are scientists and you know what a scientific statement is and you know what a political statement is. We had no problem distinguishing between the two.