HONG KONG (AP) — A landmark national security trial opened Monday in Hong Kong for prominent activist publisher Jimmy Lai, who faces a possible life sentence if convicted under a law imposed by Beijing to crush dissidents.

Lai, 76, was arrested in August 2020 during a crackdown on the city’s pro-democracy movement under the sweeping national security law enacted following huge protests four years ago. He is charged with colluding with foreign forces to endanger national security and conspiring with others to put out seditious publications.

The closely watched case — tied to the now-shuttered pro-democracy newspaper Apple Daily that Lai founded — is widely seen as a trial of press freedom and a test for judicial independence in the Asian financial hub.

China promised that the former British colony could retain its Western-style civil liberties for 50 years after returning to Chinese rule in 1997. But in recent years, the Hong Kong government has severely limited free speech and assembly and virtually eliminated political opposition under the rubric of maintaining national security. Many leading activists were arrested, silenced or forced into self-exile.

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Lai’s trial is Hong Kong’s first on charges of collusion with foreign forces. It also targets three companies related to Apple Daily.

Lai smiled at his supporters after he walked into the courtroom. Some members of the public waved at Lai to show their support. Hong Kong’s Roman Catholic Cardinal Joseph Zen, a vocal democracy advocate in the city, was among the attendees.

Three judges, approved by the government, are overseeing the proceedings. The trial is expected to last about 80 days.

Last year, six former Apple Daily executives entered guilty pleas to collusion charges, admitting to the court they conspired with Lai to call for sanctions or other hostile activities against Hong Kong or China. They were convicted and await sentencing behind bars.

Some of the former executives, alongside two others who also pleaded guilty to collusion charges, are expected to testify as witnesses for the prosecution of Lai.

Outside the court building, there was a heavy police presence. Dozens of residents queued up to attend the hearing hours before its start.

Jolly Chung, 29, was among the first in the line, saying she would try to get in to observe the proceedings whenever she can.

“As a Hong Konger, I want to witness this, even though I know he will lose,” she said.

Andy Sung, in his 40s, said he came to witness history. “Choosing to come here is a small practice of some sort of resistance,” he said.

Lai’s trial was originally scheduled to start last December but was postponed while the Hong Kong government appealed to Beijing to effectively block his attempt to hire a British defense lawyer. City authorities subsequently barred the lawyer, Timothy Owen, from representing Lai, saying it would likely pose national security risks.

Last week, Lai’s son Sebastien met with Britain’s foreign secretary, David Cameron, to lobby for Britain’s help in freeing his father, who holds British citizenship.

Cameron said in a statement that the security law is a “clear breach” of the Sino-British Joint Declaration and its continued use shows China has broken its international commitments.

British and Chinese authorities signed the agreement in 1984, stipulating that Hong Kong would retain a high degree of autonomy and freedoms for 50 years.

Cameron said he was particularly concerned by the “politically motivated prosecution” of Lai. He urged Chinese officials to repeal the security law and release Lai.

“Jimmy Lai has been targeted in a clear attempt to stop the peaceful exercise of his rights to freedom of expression and association,” Cameron said.

The U.S. condemned the prosecution of Lai and urged authorities in Hong Kong and Beijing to respect press freedom, U.S. State Department spokesperson Matthew Miller said.

“We call on Hong Kong authorities to immediately release Jimmy Lai and all others imprisoned for defending their rights,” he said.

The chairpersons of the U.S. Congressional-Executive Commission on China said in a statement that the trial is a “political prosecution plain and simple and another sad example of the Hong Kong government’s increasingly repressive policies.” They also called for Lai’s release and urged authorities to drop the charges against him.

Hong Kong, once seen as a bastion of media freedom in Asia, ranked 140th out of 180 countries and territories in Reporters Without Borders’ latest World Press Freedom Index. The group said the city had seen an “unprecedented setback” since 2020, when the security law was imposed.

Online news outlet Stand News, known for its openly critical stance against the Hong Kong government, was forced to shut down under the crackdown, with its two former top editors being charged with sedition.

The governments of both Hong Kong and China have hailed the law for bringing back stability to the city.