A classified study on the origins of COVID-19 conducted at a top U.S. biodefense facility concluded that the virus could have escaped from a laboratory in China.

The previously undisclosed report, first reported on by Sinclair, was executed by scientists at the Lawrence Livermore National Laboratory, the Department of Energy’s premier biodefense research institution. Researchers at Livermore’s “Z Division,” the lab’s intelligence unit, issued the report May 27, 2020, classified “Top Secret.”

A key takeaway from the report was that COVID-19 could have originated in a China-based laboratory, emphasizing that the theory warranted further investigation.

In an email to Sinclair, a Livermore spokesperson confirmed the existence of the report but declined to provide additional information. “Because the report you are referring to is classified,” wrote Lynda Seaver, director of public affairs, “it would be inappropriate for our lab to discuss this.”

“The Z Division report received only limited distribution at the time of its issuance, sources said, prompting some senior U.S. officials in the Trump administration to make inquiries into why it had not been brought to their attention last May. Senior officials at the Energy and State Departments were said to have intervened to quash efforts by lower-level U.S. officials who, intrigued by the Z Division report, contacted the Livermore scientists who wrote it to seek additional information,” the report added.