Eleven opposition activists, including a US citizen, were handed lengthy prison sentences yesterday for their roles in a protest at Phnom Penh’s Freedom Park last year that turned violent and left dozens injured.

In a decision that came as a surprise to many, judge Lim Makaron ruled that the Cambodia National Rescue Party members were guilty of trying to foment an “insurrection” by taking part in a demonstration led by CNRP lawmakers at the public square on July 15, 2014.

“The 11 activists were sent to jail after the lawyers boycotted the trial today,” Sam Sokong, lawyer for the defence, said after the ruling.

He added that the lawyers had boycotted the proceedings because the court had called for the trial to resume on a daily basis.

“The court did not listen to the lawyers and continued the trial.… They moved quickly and decided to issue a guilty verdict,” he said.

Meach Sovannara, a Cambodian-American and head of the CNRP’s information and media department, was convicted of “leading an insurrection” and sentenced to 20 years in jail. CNRP activists Oeur Narith and Khin Chhumroeun, the president of the party’s youth wing, received the same sentence.

Eight other party activists were sentenced to seven years for joining the “insurrection”.

Observers have long asserted that the case against Sovannara and the other activists was being used by the ruling Cambodian People’s Party to exert pressure on the opposition during the long negotiations over new laws governing elections.

In April, the activist was released on bail just hours after the formation of the new National Election Committee – a key part of the negotiations – leading some to express optimism that the case would be thrown out amid a “culture of dialogue” between Prime Minister Hun Sen and CNRP president Sam Rainsy.

Thirty-nine security personnel and at least six protesters were injured when opposition demonstrators turned on a group of notoriously violent Daun Penh district security guards at the July protest following a scuffle between the rally-goers and the advancing guards.

The main contingent of the guards quickly retreated as the protesters fought back, leaving several ill-equipped guards among them to suffer the full force of the CNRP supporters’ rage, pent up over months of violent crackdowns on opposition protests.

Sokong yesterday said that his clients should have been afforded more time to seek additional legal assistance before a sentence was passed.

“The court seemed to hatch a plot to close this case [yesterday] even though there were no lawyers present,” he said. “If lawyers boycott the court, it must give them more time.”

The case has been heard intermittently since December, with questionable evidence presented to the judge, according to rights groups.

Jamie Meach, Sovannara’s wife, who resides in the US, said yesterday that she had lost all confidence in the Cambodian justice system and would now seek urgent consular assistance from the US Embassy and from Washington if her husband wants to leave Cambodia.

“I relied on the lawyers and the court in Cambodia, but I have lost hope. So I must seek intervention from this side, but I don’t know if he will be able to come back [to the US] or not,” she said.

“If he wants to come back, I will seek help from the US Embassy and US Congress, because he is an American national. If he wants to come, it will be OK.”

Judge Makaron could not be reached for comment.

CNRP spokesman Yem Ponharith declined to comment on the decision, saying the party’s “culture of dialogue” with the CPP “is in the interests of the Khmer people”.

Rainsy, who last night left for a three-week trip to France, did not respond to a request for comment by press time.

Phay Siphan, Council of Ministers spokesman, said the detente between the two parties could not be allowed to interfere with the judge’s decision, because political leaders “do not have superiority over the courts”.

Local advocacy group Licadho decried yesterday’s proceedings as “a show trial with a predetermined ending, apparently set up only to intimidate the CNRP”, and called for the verdicts to be overturned.