“If you look at the evolution of the virus in bats and what’s out there now, [the scientific evidence] is very, very strongly leaning toward this could not have been artificially or deliberately manipulated,” Fauci told National Geographic. “Everything about the stepwise evolution over time strongly indicates that [this virus] evolved in nature and then jumped species,” and was not leaked from a lab by accident.

While China and the World Health Organization have claimed that the coronavirus initially infected humans at an outdoor market in Wuhan, several U.S. officials have floated the possibility that the coronavirus escaped from a lab. China’s only level-4 virology lab studying highly contagious diseases, the Wuhan Institute of Virology, is located about nine miles from the market where Chinese officials claim the pandemic originated, and U.S. diplomats have warned of safety weaknesses at the Institute in the past.

Secretary of State Mike Pompeo on Sunday claimed that there is “a significant amount of evidence that [the coronavirus] came from that laboratory in Wuhan.” Senator Tom Cotton (R., Ark.) has also said it’s possible that the coronavirus escaped from a Chinese lab.

“This evidence is circumstantial, to be sure, but it all points toward the Wuhan labs,” Cotton wrote in an April op-ed for the Wall Street Journal.