A multi-year investigation from Republicans on the Senate Health, Education, Labor, and Pensions Committee found a “preponderance of circumstantial evidence” that COVID-19 emerged from the Wuhan Institute of Virology (WIV) through at least one leak.

The HELP Committee report, obtained by the Daily Caller ahead of its official Tuesday release, provides “a significant amount of evidence to disprove the theory” that COVID-19 emerged from the Huanan seafood market, Kansas Sen. Roger Marshall told reporters. It emphasizes that an accidental leak, brought on by unsafe laboratory conditions, is the most likely origin of COVID-19. The report also notes that Chinese Communist Party officials engaged in a systematic coverup that delayed the world’s response to the virus by weeks, if not months.

China’s vaccine development timeline suggests multiple leaks from WIV, according to the full report. Professor Zhou Yusen, a People’s Liberation Army doctor who mysteriously disappeared and died in 2020, filed for the first COVID-19 vaccine patent in February 2020. His development of the vaccine would have taken “at least two to three months,” according the report, signaling a start date of no later than November 2019. China asserts that COVID-19 was first detected on December 8, 2019.

“The virus is circulating in November. They’re closing schools in November and December,” Marshall noted. “The theory is there is an initial lab leak. They’re able to contain it, but they start developing the vaccine.”

“The timeline shifts a little bit earlier. I think that’s the theme here from this report. It shifts earlier. I think the two lab leak theory is the best conclusion we can get here,” he continued.

The State Department previously alleged in a January 2021 fact sheet that WIV researchers became ill in the fall of 2019, displaying “symptoms consistent with both COVID-19 and common seasonal illnesses.” WIV researcher Shi Zhengli had claimed that WIV researchers and students had displayed “zero” coronavirus infections. (RELATED: Wall Street Journal Leaves Out Crucial Detail In Report On China’s ‘Bat Woman’)

The report pinpoints shoddy workmanship and design as key factors in the leak. Although French scientists and engineers with the Jean Merieux BSL–4 laboratory were supposed to oversee construction at WIV, Chinese scientists and officials reportedly boxed them out of development after they submitted initial plans. The Chinese scientists and officials made structural changes to the French design that created more opportunities for a virus to leak out and used construction materials that were improper for containing aerosol viruses, according to the report.

Despite funding the lab extensively through the non-profit EcoHealth Alliance, U.S. officials never visited WIV. They were therefore putatively unaware of the type of research it conducted until EcoHealth Alliance informed the National Institutes of Health about gain-of-function research conducted in 2018 and 2019. The group violated the terms of its grant by not immediately informing the U.S. government of its activities.

“No one from EcoHealth had hands-on experience at the WIV. Daszak had never been there. He himself says, I never needed to look at the data, they gave me what I needed to see,” Marshall said. “If we’re funding something, I’m not sure they need to be there every day, but we should have American scientists over there.”

Marshall also noted the federal government’s narrow definition of gain-of-function research, arguing that limits imposed by the HHS Framework for Guiding Funding Decisions about Proposed Research Involving Enhanced Potential Pandemic Pathogens (P3CO) are not restrictive enough. (RELATED: GOP Senators Review US Government’s Funding, Promotion Of Research That May Have Caused COVID-19)

“I’ve read what the new definition is five times, and I’m going to have to get some lawyers to explain to me what it is. I think it’s their get-out-of-jail-free card,” he said.

Marshall, an OB/GYN, praised the HELP Committee staffers who prepared the report.

“They followed the scientific method. You put out a hypothesis and for the most part you try to disprove that hypothesis,” he said. “They exhausted every piece of evidence they could find.”

However, the senator added, a number of significant questions remain unanswered due to China’s reported obstruction, as well as the Executive Branch’s refusal to provide unredacted documents to the committee. President Joe Biden signed legislation in March that declassifies intelligence data surrounding COVID-19’s origin. The FBI views a lab leak as the virus’ most likely origin with “moderate confidence,” and the Energy Department maintains “low confidence” in a lab leak.

“Why didn’t the DOD go back and do retrospective blood tests on the military folks that went [to the 2019 Wuhan Military Games] and then show it to us? This is part of the dark, dark tunnel that I can’t get access to.”