A former British marine charged with spying for Hong Kong’s intelligence service has died, according to a police statement released on Tuesday evening.

The man, who was named by the Thames Valley Police as Matthew Trickett, was found dead in a park in Maidenhead, a town west of London, on Sunday. Mr. Trickett was one of three men charged last week under Britain’s National Security Act with assisting the Hong Kong intelligence service, and their case was expected to return to court on Friday.

Hong Kong is a former British colony and a special administrative region of China, and tensions between London and Beijing have been ratcheting up in recent months as the British government has become increasingly vocal over allegations of Chinese espionage. In the wake of the charges last week, Britain summoned the Chinese ambassador for a reprimand.

Mr. Trickett, 37, who was a British immigration enforcement officer and a former Royal Marine, was also the director of a private security firm, MTR Consultancy.

According to the police, a member of the public alerted the authorities to a situation in Grenfell Park in Maidenhead on Sunday about 5:15 p.m. Mr. Trickett, who was from the area, was found and, despite the efforts of emergency responders, was pronounced dead at the site.

“An investigation is ongoing into the death, which is currently being treated as unexplained,” the police said in a statement, adding that “a post-mortem will be conducted in due course.”

The police have appealed to the public for any information that could help in their investigation.

In a statement provided to Reuters, Mr. Trickett’s family said they were “mourning the loss of a much-loved son, brother and family member.”

Mr. Trickett had been released on bail after being charged with assisting a foreign intelligence service and with foreign interference. The Metropolitan Police said in a statement last week that “the foreign intelligence service to which the above charges relate is that of Hong Kong.”

The conditions of Mr. Trickett’s bail required him to register at a police station regularly, according to the Thames Valley Police. He was awaiting court hearings that were set to begin on Friday in London’s central criminal court.

China’s crackdown on protesters and other advocates for democracy in Hong Kong has driven hundreds of thousands of people to seek refuge elsewhere over fears that they could be persecuted.

Since 2021, Britain has allowed some Hong Kong residents to settle in the country under a special visa program, and more than 160,000 people, including high-profile activists, have arrived.