More than a year ago, the first case of the coronavirus was detected somewhere in or around Wuhan, in the Chinese province of Hubei. Although almost from the start of the pandemic, leading health organizations, alongside global leaders have called for international investigators to be allowed into China to find out how it all started, Beijing has several times rejected calls for an independent inquiry into the origin of the coronavirus, facing a barrage of criticism at home and abroad.

Deep in the lush valleys of southern China lies the entrance to a mine shaft that once harbored bats carrying the closest known relative to COVID-19. The area is of intense interest because it may hold clues to the origins of the coronavirus that has killed more than 1.7 million people worldwide but it has instead become a black hole void of information due to political sensitivity.

A bat research team that visited recently had their samples confiscated, two people familiar with the matter said. A team of Associated Press journalists (AP) was tailed by plainclothes police in multiple cars who blocked access to sites in late November.

The investigation showed the Chinese government is strictly controlling all research into the virus's origins while promoting fringe theories that the pandemic originated elsewhere.

The government is monitoring scientists’ findings and mandating that the publication of any research first be approved by a new task force managed by China’s cabinet under direct orders from President Xi Jinping, according to internal documents obtained by AP.

A rare leak from within the government, the dozens of pages of unpublished documents confirm what many have long suspected: The clampdown comes from the top. The investigation was based on interviews with Chinese and foreign scientists and officials, along with public notices, leaked emails and unpublished documents from China’s State Council and the Chinese Center for Disease Control and Prevention (CDC). It reveals a pattern of government secrecy and top-down control that has been evident throughout the pandemic.

"They only select people they can trust, those that they can control," said an expert who works with the Chinese CDC, declining to be identified out of fear of retribution. China’s foreign ministry said in a fax that "the novel coronavirus has been discovered in many parts of the world" and research should be carried out "on a global scale."

China’s leaders aren’t alone in politicizing research into how the pandemic started. In April, U.S. President Donald Trump shelved a U.S.-funded project to identify dangerous animal diseases across Asia.

Research into COVID-19’s origins is critical to preventing future epidemics, and the lack of openness severed ties between Chinese and U.S. scientists. Although the World Health Organization (WHO) says it will send a team to China in January to investigate, its members and agenda had to be approved by China.

The probe into how the coronavirus first emerged started in the Huanan Seafood Market in Wuhan, a sprawling complex where many of the first human cases were detected. In mid-December last year, Huanan vendor Jiang Dafa noticed people were falling ill, including a worker who helped clean carcasses at a stall and later died. At first, the China CDC moved swiftly. On Jan. 1, the market was ordered shut, barring vendors from fetching their belongings, Jiang said.

Internal China CDC data shows that by Jan. 10, researchers were sequencing environmental samples. In late January and early February, as the virus spread rapidly, Chinese scientists published a burst of research papers on COVID-19. Then one paper proposed without concrete evidence that the virus could have leaked from a Wuhan laboratory near the market. It was later retracted, but it raised the need for image control.

An internal notice from a Chinese CDC lab issued Feb. 24 put in new approval processes to standardize publication under "important instructions" from Chinese President Xi Jinping. Other notices ordered CDC staff not to share any data, specimens, or other information related to the coronavirus with outside institutions or individuals. In early March, China’s cabinet, the State Council, centralized all COVID-19 publications under a special task force.

The notice, obtained by the AP and marked "not to be made public," was sweeping in scope, applying to all universities, companies and medical and research institutions. It said communication and publication of research had to be orchestrated like "a game of chess" under instructions from Xi and guided by propaganda and public opinion teams. The order went on to warn that those who publish without permission, "causing serious adverse social impact, shall be held accountable."

After the secret orders, the tide of research papers slowed to a trickle. Though the Chinese CDC returned to collect some 2,000 samples from the market over the following months, nothing was published. On May 25, Chinese CDC chief George Gao said no animal samples from the market had tested positive, ruling it out as the source.

With the market proving a dead end, scientists turned their attention to hunting for the virus at its likely source: bats. Nearly 1,000 miles (1,610 kilometers) away from Wuhan, bats inhabit a maze of underground limestone caves in Yunnan province.

The coronavirus’s genetic code is strikingly similar to bat coronaviruses, and scientists suspect COVID-19 jumped into humans from a bat or an intermediary animal. Chinese scientists quickly started testing animals suspected of carrying the coronavirus.

Records show scientist Xia Xueshan received a 1.4 million RMB ($214,000) grant to screen animals in Yunnan for COVID-19.

In February, his team took samples from animals including bats, snakes, bamboo rats and porcupines. But the government restrictions soon kicked in; data on the samples has not been released. Today, the caves in Yunnan home to the closest viral relative of the coronavirus are under close watch.

Security agents tailed the AP team in three locations and stopped journalists from visiting the cave where researchers identified the bats responsible for SARS. Chinese state media has instead aggressively promoted theories suggesting the virus originated elsewhere, such as via frozen seafood, a hypothesis WHO and others have dismissed.

The government is also limiting and controlling the search for the first human cases through the retesting of flu samples.

Hundreds of Chinese hospitals collect samples from patients with flu-like symptoms, storing them for years. The samples could easily be tested again for COVID-19, although politics could determine whether the results are made public, said Ray Yip, the founding director of the Chinese CDC.

Researchers in the U.S., Italy, France and elsewhere have already combed through some of their archived samples to identify the earliest cases of COVID-19 in late 2019. But in China, scientists have only published retrospective data from two Wuhan flu surveillance hospitals, out of at least 18 in Hubei province and more than 500 across the country.

The little information that has trickled out suggests COVID-19 was circulating beyond Wuhan in 2019, a finding that could raise awkward questions for Chinese officials about their early handling of the outbreak. Peter Daszak of the EcoHealth Alliance said identifying the pandemic’s source should not be used to assign guilt. "We’re all part of this together," he said. "Until we realize that, we’re never going to get rid of this problem."