“A man shouted, ‘I will bomb you, your wife and your son to death’, and then hung up. The office then reported the matter to police,” the insider said.

A police spokesman said the case was listed as criminal intimidation, confirming that a threatening call had been received by a judicial office in West Kowloon Court on Thursday.

“An investigation by the Sham Shui Po district anti-triad squad is under way. No arrests have been made yet,” the spokesman said.

Lai’s case has drawn global attention, with US Secretary of State Mike Pompeo, on the same day as the hearing, accusing the Chinese Communist Party of using the courts to silence peaceful dissent, a tactic he described as “a hallmark of authoritarian regimes”. He also said the United States was appalled by the Hong Kong government’s political persecution of “courageous” pro-democracy advocates.

After the threatening call came to light, Hong Kong’s Department of Justice confirmed that a judicial officer had been intimidated while performing his duties, with his family members threatened in an attempt to influence court decisions.

“The [Hong Kong] government and any law-abiding jurisdiction will not tolerate such violent and illegal acts. Police are taking resolute enforcement action so as to apprehend the culprit as soon as possible and safeguard the city’s public peace and safety,” the department said in a statement.

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Law Society president Melissa Pang expressed shock over the incident, saying using illegal means hoping to influence a court decision was not only a challenge to the rule of law, but also a serious criminal act. She said the courts and judges handled each case in accordance with the law, regardless of its nature or the person involved. Pang urged the government to handle all illegal acts seriously.

So’s personal data has also been circulating on messaging groups. The justice department reminded the public of the injunction forbidding the unlawful and wilful doxxing of judicial officers and their families. Any person who violated the interim injunction order could be held in contempt of court, it added.

So is not the first member of the judiciary to be singled out for criticism. On New Year’s Day, Madam Justice Anthea Pang Po-kam’s name in Chinese was painted outside the High Court in Admiralty, along with the accusation that she was a “judge with a red background”, an apparent reference to the Chinese Communist Party.

The Bar Association and Law Society jointly condemned the graffiti, calling it “outrageous” and refuting suggestions that court rulings were politically influenced.

Lai, Royston Chow Tat-kuen and Wong Wai-keung – both senior executives at Next Digital, the parent company of Lai’s Apple Daily newspaper – were charged with defrauding a government-owned enterprise by breaching land-lease terms. Wong and Chow were released on bail.

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All three were arrested by the police force’s national security unit in a high-profile operation that saw more than 200 officers raid the company’s Tseung Kwan O offices on August 10. So granted the search warrant.

The new police unit initially cited alleged collusion with foreign forces – an offence under the security law – in apprehending the three along with a handful of other Lai associates, but ultimately did not lay any charges stemming from the controversial legislation on Thursday.

Since the national security law was imposed by Beijing on June 30, police have so far arrested 24 men and 8 women, and charged two people.

So also handled the first prosecution under the law for publicly chanting pro-independence slogans. That defendant was accused of incitement to commit secession at West Kowloon Court.