A Hong Kong journalist who investigated police conduct during a mob attack has been found guilty of making false statements in a prosecution critics said sent a chilling warning to the local press.

Bao Choy, a 37-year-old award-winning journalist for government broadcaster RTHK, was fined HK$6,000 (US$773).

A freewheeling press has for decades marked the city’s autonomy from the mainland as part of the “one country, two systems” principle promised to Hong Kong after the handover from the UK to China in 1997.

But authorities are cracking down on anything perceived as dissent in Hong Kong in response to anti-government protests in 2019. The prosecution of Choy has stoked fears about press freedom just as pro-Beijing groups call for independent outlets to be shut altogether.

Choy worked on an investigative documentary examining the police response to a bloody July 2019 attack on pro-democracy activists by a mob after officers were accused of arriving too late to protect them.

Ivy Chui, the magistrate, said on Thursday that Choy “knowingly” made a false statement when she was accessing a public database of vehicle licence plate information during her investigation.

“Today the decision of the magistrate is a very heartbreaking one,” Choy said outside court. “Even though I was convicted, I don’t see journalism as a crime.”

The Hong Kong Journalists Association said reporters routinely used public databases and that Choy’s arrest was an attack on press freedom. Pro-democracy lawmakers added that the trial was meant to dissuade journalists from conducting controversial investigations.

Beijing has targeted the media after its critical coverage of the government’s handling of the 2019 protests that represented one of the biggest internal challenges to the Chinese Communist party’s rule.

Jimmy Lai, the owner of Apple Daily, the pro-democracy newspaper, and an outspoken critic of Beijing, was jailed for 14 months last week.

A day later, Chris Tang, the police chief, said Apple Daily “incited hatred” by publishing a photo of children playing with toy guns at an event promoting Hong Kong’s new education policies as part of the national security law introduced last year. He highlighted the coverage as he backed new laws to regulate “fake news”.

“For the time being, there’s no specific law on fake news, right? And there’s no legal definition about fake news,” Tang told local broadcaster TVB. “I think it’s good to have such a law. For every law that can assist national security and assist us to make Hong Kong more safe.”

Ta Kung Pao, a pro-Beijing newspaper, recently printed a commentary calling for Apple Daily to be outlawed to “plug loopholes” in the city’s national security defences.

At the same time Chinese government-backed media continues to expand in the city, which analysts said was part of a co-ordinated effort to shift public opinion.

Bauhinia Culture, a state-backed publisher, this week acquired a stake in Hong Kong TV station Phoenix Media. The state-owned enterprise, run by Mao Chaofeng, the former vice-governor of Hainan province, was set up in 2019.