After a three-year trial, in which the judge determined that Kem Sokha’s election campaigns and activity in civil society were intended to inspire a “colour revolution,” the opposition leader in Cambodia was convicted guilty of treason and sentenced to 27 years under house imprisonment.

The former leader of the Cambodia National Rescue Party (CNRP) was informed by the court at the Phnom Penh Municipal Court that he would be prohibited from politics and election voting indefinitely. And while he was under house arrest, he was not permitted to meet anyone outside of his family.

Kem Sokha was arrested in September 2017 without a warrant in a midnight raid on his home and taken to a provincial jail. Denied bail several times before eventually being released under house arrest, the prominent politician was charged with “conspiracy with a foreign power” under article 443 of Cambodia’s criminal code.

In his decision on Friday, presiding Judge Koy Sao said the court found Kem Sokha guilty of secretly colluding with foreigners to instigate a “colour revolution” in Cambodia under the pretext of campaigning for democratic elections.

The judge said that Kem Sokha was taking ideas from other countries and had used a non-governmental organisation he had founded – the highly-respected Cambodian Center for Human Rights – to further his plans.

“The accused activity is an illegal act that affected the peace, national security, stability and the happiness of the people,” the judge said.

Kem Sokha did not react as his sentence was announced, and he did not take questions from reporters after the verdict, instead he gave a slight smile and raised a fist as he was escorted out of the court’s side door by security guards.

Outside the courtroom, defence lawyer Ang Udom told reporters the verdict was unjust and the case was politicised.

“We all already knew that this is a political case and only the politicians can decide [it],” Ang Udom said, adding he and other lawyers would meet with Kem Sokha later to discuss an appeal.

Condemnation of the verdict was swift.

United States ambassador to Cambodia, W Patrick Murphy, tweeted that Washington was “deeply troubled” by the conviction.

“[Kem Sokha’s] trial, built on a fabricated conspiracy, was a miscarriage of justice,” Murphy wrote. “Inclusive democracy would further the Cambodian people’s aspirations for a prosperous society that respects all voices and rights.”

Kem Sokha had consistently denied the charges against him, saying he was only trying to win power in Cambodia through the ballot box.

Al Jazeera’s Tony Cheng, reporting from Bangkok, said Kem Sokha’s guilty verdict did not come as a surprise in a trial that had taken three years to complete and involved charges which had seen the opposition leader either held in detention or under house arrest since 2017.

“It seemed very unlikely there was going to be any leniency or certainly any chance of walking out of court today a free man,” Cheng said of the verdict.

“Nonetheless, the 27-year sentence on what, I think most people accept, are very trumped up charges seems very severe,” he said.

“This is effectively a life sentence” for the 69-year-old opposition leader, he added.

Kem Sokha’s popular CNRP was dissolved in 2017 and the government, under longtime ruler and Prime Minister Hun Sen, even made it a crime to associate with the name or depict images of the defunct party and its leaders.

Without any effective opposition, Hun Sen’s Cambodian People’s Party (CPP) swept the board in national elections in 2018.