Rumours abounded on Friday night that China's top spycatcher had defected to the US, amid a growing focus in Washington on the theory that Covid-19 escaped from a Wuhan laboratory.
Dong Jingwei, vice minister of state security, was reported to have flown from Hong Kong to the US in February with his daughter. There was no confirmation of the rumoured development from either the US or China.
Dr Han Lianchao, a former Chinese foreign ministry official who is now a pro-democracy activist in the US, claimed Dong had defected.
Dr Han, of the Citizen Power Initiative for China in Washington, claimed the situation was discussed by senior Chinese and US officials when they met in Alaska in May.
Nicholas Eftimiades, a former CIA and Pentagon expert on China, told the SpyTalk newsletter, which first reported the alleged development, that Dr Han was "trusted for his integrity".
However, he said the suspected defection was “exactly what it is, a rumour". He said such rumours about Chinese officials defecting "happen all the time” and were not necessarily correct.
If Dong has indeed defected, he would be the most high-profile Chinese official ever to do so. The 57-year-old assumed responsibility for counter intelligence three years ago as China's top spycatcher.
Despite the official silence from China, the social media account of its top law enforcement agency, the Central Political and Legal Affairs Commission, claimed Dong had spoken at a counter-espionage seminar on Friday, cautioning spies to watch out for "insiders" who collude with "anti-China" forces and for “people who bankroll their activities behind the scene”.
The agency did not say where the alleged seminar had taken place, according to the South China Morning Post.
The rumour came as Washington continues to struggle to find the truth about the origins of Covid-19. Last month, President Joe Biden ordered the US intelligence community to deliver in 90 days a report on how it started.
Mr Biden said US officials had already "coalesced around two likely scenarios": that it passed from animals to humans, or was a laboratory accident at the Wuhan Institute of Virology.
‘We've been looking for needles in haystacks’
One former senior US government official, who worked on an investigation into the Wuhan laboratory theory under Donald Trump's administration, told The Telegraph the only way to prove it would be to encourage defectors.
He said: "If you offer $5 million and citizenship there'll be plenty of people wanting to defect. We've been sitting on our ass for a year and a half looking for needles in haystacks.
"We need human intelligence. We need to hear from Chinese people who were direct witnesses. Then you're off to the races." He added: "We have a lot of reason to be suspicious it was a lab leak. We should be treating this like a potential crime scene.
"I've never seen a bigger whitewash. China's approach has been systematic cover-up and denial. If this had started in a lab in Oxford you can bet the UK government would be responsive to us."
The former official added: "People get executed for [messing up] in China. So it is possible the Wuhan people covered it up from their own government."
This week, Shi Zhengli, the Wuhan coronavirus researcher known as China's bat woman, gave a brief interview to the New York Times, in which she vehemently denied the outbreak started at the lab.
She said: "How on Earth can I offer up evidence for something where there is no evidence? I don’t know how the world has come to this, constantly pouring filth on an innocent scientist. I’m sure that I did nothing wrong."
Any defection would be embarrassing for the Chinese Communist Party ahead of its centenary on July 1. Propaganda has been ramping up and large boards with a red-emblazoned "100" have been hung above shops and along busy streets.
The Chinese Communist Party has more than 91 million members.
Next month's anniversary celebrations will see the release of a blockbuster film about the party's founding. Key party members will also receive a special medal at a ceremony in Beijing.