Anthony Fauci, the retiring top official in the United States response to the Covid-19 pandemic, said Sunday he has “a completely open mind” about the origins of the respiratory virus.

“I have a completely open mind about that, despite people saying that I don’t,” Fauci said, when asked on NBC’s “Meet the Press” about the theory that the virus may have leaked from a lab in China in 2019.

Fauci acknowledged that a group of international, respected virologists has written that strong evidence shows the virus jumped from animals to humans, but said it “hasn’t been definitively proven.”

“Even when there’s nothing to hide, they act in a suspicious, non-transparent way,” Fauci said of the Chinese government.

A report this fall from Vanity Fair and ProPublica, which said the Wuhan Institute of Virology dealt with an unspecified emergency at the time Covid-19 began, brought back to the forefront a debate about whether the virus might have come from a lab.

Speaking on CBS’ “Face the Nation” in a separate interview Sunday, Fauci said he’d like to know “all of the details of what went on with the original people who were infected.”

On “Meet the Press,” he also criticized that government’s strict ongoing response to Covid-19, which has sparked recent protests among people in China.

“Their approach has been very, very severe and rather draconian in the kinds of shutdowns without a seeming purpose,” Fauci said to host Chuck Todd.

Ashish Jha, coordinator of the White House’s Covid-19 response, added Sunday on ABC’s “This Week” that “lockdown and zero Covid is going to very difficult to sustain.”

Chinese government officials, under President Xi Jinping, have adopted a “zero Covid” policy against the disease, resulting in widespread lockdowns and travel restrictions in recent days.

Sen. Chris Murphy (D-Conn.), a member of the Foreign Relations Committee, said Sunday on CNN’s “State of the Union” he didn’t yet know whether the protests would amount to a real threat against Xi’s leadership.

“These dictators unfortunately have pretty sophisticated means of staying in power,” Murphy said.