(Bloomberg) -- A man charged in a UK espionage case for assisting a foreign intelligence service from Hong Kong has died for “unexplained” reasons, British police said.

Matthew Trickett, 37, was pronounced dead at the scene Sunday at Grenfell Park in Maidenhead, according to Thames Valley Police. The town is located less than 30 miles (48 kilometers) west of London. Officers found Trickett after responding to a report from a member of the public, the force said.

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

Trickett, a private investigator, was charged with assisting a foreign intelligence service and foreign interference under the National Security Act last week, along with Chi Leung Wai, a UK Border Force Officer and Chung Biu Yuen, an office manager at the Hong Kong Economic and Trade Office in London. 

The next hearing is scheduled for May 24 at the Old Bailey. 

Trickett was on bail and required to register at a police station regularly, said Thames Valley Police. 

Police are now seeking information from the public, especially “anyone who was in Grenfell Park on Sunday afternoon prior to 5:15 p.m.”

China’s embassy in the UK condemned the British authorities’ “fabrication of the so-called case” in a statement Monday.

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