An expert group charged by the World Health Organization to investigate how the COVID-19 pandemic started released its final report Friday, reaching an unsatisfying conclusion: Scientists still aren't sure how the worst health emergency in a century began.

At a press briefing on Friday, Marietjie Venter, the group’s chair, said that most scientific data supports the hypothesis that the new coronavirus jumped to humans from animals.

That was also the conclusion drawn by the first WHO expert group that investigated the pandemic’s origins in 2021, when scientists concluded the virus likely spread from bats to humans, via another intermediary animal. At the time, WHO said a lab leak was “extremely unlikely.”

Venter said that after more than three years of work, WHO’s expert group was unable to get the necessary data to evaluate whether or not COVID-19 was the result of a lab accident, despite repeated requests for hundreds of genetic sequences and more detailed biosecurity information that were made to the Chinese government.

“Therefore, this hypothesis could not be investigated or excluded,” she said. “It was deemed to be very speculative, based on political opinions and not backed up by science.” She said that the 27-member group did not reach a consensus; one member resigned earlier this week and three others asked for their names to be removed from the report.

Venter said there was no evidence to prove that COVID-19 had been manipulated in a lab, nor was there any indication that the virus had been spreading before December 2019 anywhere outside of China.

“Until more scientific data becomes available, the origins of how SARS-CoV-2 entered human populations will remain inconclusive,” Venter said, referring to the scientific name for the COVID-19 virus.

WHO Director-General Tedros Adhanom Ghebreyesus said it was a “moral imperative” to determine how COVID began, noting that the virus killed at least 20 million people, wiped at least $10 trillion from the global economy and upended the lives of billions.

Last year, the AP found that the Chinese government froze meaningful domestic and international efforts to trace the virus' origins in the first weeks of the outbreak in 2020 and that WHO itself may have missed early opportunities to investigate how COVID-19 began.

U.S. President Donald Trump has long blamed the emergence of the coronavirus on a laboratory accident in China, while a U.S. intelligence analysis found there was insufficient evidence to prove the theory.

Chinese officials have repeatedly dismissed the idea that the pandemic could have started in a lab, saying that the search for its origins should be conducted in other countries.

Last September, researchers zeroed in on a short list of animals they think might have spread COVID-19 to humans, including racoon dogs, civet cats and bamboo rats.