The hearing opened at 2.30 p.m. local time (12.30 p.m. GMT). The trial is expected to last a day and the verdict will be reserved. Mr. Rainsy is being prosecuted for comments made on Facebook in June 2019.

Co-founder of the National Salvation Party of Cambodia (PSNC), the main opposition party, Sam Rainsy, 73, fought Hun Sen for a long time – in power for 37 years in Cambodia – before going into exile in France where he has lived since 2015 .

Mr. Rainsy, who also has French nationality, is already the subject of numerous trials in Cambodia, where he says he is being prosecuted for political reasons.

In 2019, he had tried, in vain, to return to Cambodia, a project perceived as “an attempted coup” by the authorities.

On his arrival at court on Thursday, surrounded by supporters, the opponent, in a suit with a tie and thin glasses, told AFP that he expected “real justice” from French justice.

In the courtroom, many people from the Cambodian diaspora were present to watch the trial.

According to the complaint filed in Paris, Sam Rainsy accused Hun Sen of being behind the death in 2008 of Commissioner Hok Lundy – head of the Cambodian national police – killed in the fall of his helicopter.

“Hun Sen assassinated Hok Lundy by means of a bomb placed inside his helicopter causing an explosion during his flight over the province of Svay Rieng, on November 09, 2008. Hun Sen decided to assassinate Hok Lundy because he knew too much about Hun Sen’s misdeeds,” Rainsy said on Facebook.

– “Political fight” –

Mr. Rainsy is also on trial Thursday for another defamation complaint, filed by Dy Vichea, for comments also made on Facebook in June 2019 by the opponent. Son of Hok Lundy, Dy Vichea is Deputy Commissioner General of the Cambodian National Police and son-in-law of Prime Minister Hun Sen.

Contacted Wednesday by AFP, Luc Brossolet, one of Hun Sen and Dy Vichea’s lawyers, said he was waiting for the “court to judge the comments concerned and criticized to be defamatory”.

For her part, Jessica Finelle, Sam Rainsy’s lawyer, told AFP that she expected the court “to recognize that it was in the general interest for Sam Rainsy to denounce the crimes committed by Hun Sen, who exercises ( functions) within the framework of a state dictatorship”.

“Sam Rainsy has been persecuted for thirty years by Hun Sen. The only weapon he has left is his freedom of expression to testify to what he has experienced and to condemn what political opponents and defenders of the human rights in Cambodia,” she added.

“Sam Rainsy is the victim in his country of a proliferation of procedures, the regime is trying to muzzle him,” Mathias Chichportich, also a lawyer for Mr. Rainsy, told AFP on Wednesday. “We expect this trial to enshrine Sam Rainsy’s right to express his political struggle,” he said.

The PSNC party had made a breakthrough in the 2013 elections before being disbanded four years later.

Since the 2018 legislative elections, after which Hun Sen’s party won all the seats in parliament, results hotly contested, the regime has multiplied arrests and procedures against any dissenting voice.

In June, during a mass trial, dozens of opposition figures were convicted, including Mr. Rainsy, sentenced to eight years in prison in absentia. This sentence is in addition to those to which he had already been sentenced, in particular 25 and 10 years in prison for having tried to overthrow the Prime Minister.

The next elections in Cambodia are scheduled for next July.

Hun Sen will run for a new term. He wants his eldest son Hun Manet, a general trained in Britain and the United States, to take over one day, but did not give a date for this potential succession.