Hong Kong’s top court on Thursday overturned the convictions of three people for refusing to hand information to the police in a national security investigation.

The Court of Final Appeal unanimously ruled the trio, who were members of the now-disbanded Hong Kong Alliance in Support of Patriotic Democratic Movements in China, did not have a fair trial.

Implementation rules under the national security law require suspects deemed to be "foreign agents" to hand over information to police.

Chow Hang-tung, Tang Ngok-kwan and Tsui Hon-kwong were jailed in 2023 for four-and-a-half months each for refusing such a request about their former organisation.

But the top court found the evidence used by prosecutors to establish that the group was acting as a "foreign agent" was so heavily redacted that it was "self-defeating".

"It was self-defeating to have redacted out the only material relied on for establishing the foreign agent element of the offence, so that, in its absence, the charge could not be proved," the judges, led by Chief Justice Andrew Cheung, wrote.

"[D]epriving the appellants of all knowledge of the nature of the prosecution’s case... made it impossible for them to have a fair trial."

The court therefore quashed the three's convictions and jail sentences.

A separate security trial of inciting subversion involving Chow and two former Alliance leaders is still pending.