LONDON (AP) — A man charged with assisting Hong Kong authorities with gathering intelligence in the United Kingdom has died in unexplained circumstances, British police said Tuesday.

Matthew Trickett, 37, was one of three men charged earlier this month with agreeing to engage in information gathering, surveillance and acts of deception that were likely to materially assist the Hong Kong intelligence service from late 2023 to May 2. Prosecutors also alleged that the men forced entry into a U.K. residential address on May 1.

The men had all been bailed and were next due to appear at London’s Central Criminal Court for a hearing on Friday. They haven’t yet entered pleas.

Thames Valley Police said Trickett was found dead in a park in Maidenhead, west of London, on Sunday afternoon after a report from a member of the public.

Police said that an investigation is ongoing into the death, which is being treated as unexplained.

British media reports said Trickett was formerly a Royal Marine who recently worked as a Home Office immigration enforcement officer. He was also reportedly the director of a security consultancy.

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He was charged along with Chi Leung (Peter) Wai, 38, and Chung Biu Yuen, 63. The men appeared at a brief court hearing to confirm their identities on May 13.

Hong Kong authorities have confirmed that Yuen was the office manager of the Hong Kong Economic and Trade Office in London.

Trickett’s lawyer, Julian Hayes, said he was “shocked” at Tuesday’s news and was supporting Trickett’s family. He declined to comment, because investigations were ongoing.

A police cordon remained in place in Grenfell Park in Maidenhead late Tuesday, with several officers stationed next to a black forensics tent located close to a children’s playground.

Chinese authorities in both the U.K. and Hong Kong have decried the charges, saying they were the latest in a series of “groundless and slanderous” accusations that the U.K. government has leveled against China.

Hong Kong’s government demanded that the U.K. provide full details on the allegations and protect the rights of the office manager of the trade office.

The spying charges came amid simmering tensions between Britain and China. U.K. officials have been increasingly vocal in warning about security threats from Beijing, and recently accused China of being behind a string of cyberespionage operations targeting politicians and Britain’s election watchdog.

Prime Minister Rishi Sunak has said Britain is facing an increasingly dangerous future because of threats from an “axis of authoritarian states,” including Russia, China, Iran and North Korea.

In a separate and ongoing court case, two men, including a parliamentary researcher, were recently charged with spying for China. Christopher Cash and Christopher Berry were charged with violating the Official Secrets Act by providing information or documents that could be “useful to an enemy” — China — and “prejudicial to the safety or interests” of the U.K. between late 2021 and February 2023.

Hong Kong, a former British colony, returned to Chinese control as a semiautonomous territory in 1997.

More than 100,000 Hong Kongers have moved to the U.K. since Beijing imposed a sweeping national security law triggered by the huge anti-government protests in the city in 2019. Britain’s government has established a fast-track immigration route for the migrants, many of whom want to settle in the U.K. because of dwindling civil liberties in their home city.

Rights groups have warned that Hong Kongers who have moved to Britain continue to face “transnational repression” by supporters of the Chinese government.