Too many questions are still unanswered about the origins of the pandemic. Though China’s doors remain closed, there are significant and promising avenues for investigation in the United States.

The two major hypotheses for the virus origins are zoonotic spillover, from an animal to human perhaps with an intermediate host, or that it leaked or escaped from a laboratory accident in Wuhan. The Wuhan Institute of Virology (WIV) is one of the world’s major centers of study of bat coronaviruses, and was developing genetically-modified variants able to infect human lung cells.

Zoonotic spillover is a plausible explanation based on historical experience, and scientists should pursue it vigorously. But similar efforts must be made to discover whether a laboratory release or infection led to the pandemic. Peter Daszak, the president of EcoHealth Alliance, a nonprofit based in New York, organized a five-year research program funded by the U.S. National Institutes of Health to study bat coronaviruses and potential spillover risk to people, with significant participation by the WIV and its scientist, Shi Zhengli. The government of China, Ms. Shi and Mr. Daszak all insist the laboratory could not be the source of the pandemic strain. Mr. Daszak has been particularly aggressive in promoting the zoonotic spillover hypothesis and attacking the laboratory leak as a “conspiracy theory.”

Last week, it was disclosed that the EcoHealth Alliance in August filed a report on its research in 2018-2019 — the report was two years late. This just happens to be the two-year period of the pandemic and intense debate about the virus origins. No reason has been given. Mr. Daszak did not respond to our query. The tardy report describes experiments, approved in advance by the NIH, to test the infectivity of the genetically-manipulated viruses on mice with cells resembling those of the human respiratory system. The manipulations made the viruses more lethal to the mice. Although the NIH continues to insist this did not fit the definition of “gain of function” research, and could not have led to the pandemic strain, it certainly should have met the U.S. government’s own requirements for stricter oversight.

Still, much is unknown. There is no direct evidence of zoonotic spillover, nor of a laboratory leak.

But unanswered questions keep emerging about Mr. Daszak and the WIV. He was at the center of public debate over virus origins, the only American appointed to the joint World Health Organization-China mission. Why did he not disclose his 2018 proposal to the Defense Advanced Research Projects Agency (DARPA) for research on bat coronaviruses with the WIV and others, which called for engineering a modification onto spike proteins of chimeric viruses that would make them infect human cells in the way the pandemic strain did? What does he know about the databases of viruses that WIV took offline in 2019 and never brought back? Does he know what research the WIV may have done on its own, during or after their collaboration? What was being done at WIV in the months before the pandemic?

Mr. Daszak must answer these questions before Congress. His grants were federal funds, and it is entirely appropriate for Congress to insist on accountability and transparency. He might also help the world understand what really happened in Wuhan.