One of Turkey’s most famous prisoners made his final appeal for freedom on Friday, at the culmination of a years-long trial that has come to define Ankara’s tense ties with Western allies.

Paris-born activist and philanthropist Osman Kavala, 64, was a relative unknown when he was detained on his arrival at Istanbul’s airport in October 2017. Kavala’s imprisonment without a conviction has become a focus of Western worries about the Turkish government’s crackdown on dissent.

“The fact that I have spent 4.5 years of my life in prison is a loss that cannot be compensated,” Kavala told the court on Friday speaking via a video link from prison.

“The only thing that would console me is the possibility that what I have gone through helps to put an end to grave judicial mistakes,” he said.

The courtroom was packed with some 200 people, including opposition members, rights groups and Western diplomats.

The prosecution wants Kavala found guilty of “attempting to overthrow” Turkish President Recep Tayyip Erdogan’s government by financing a wave of 2013 protests and then being directly involved in a 2016 coup plot.

Kavala was acquitted of the first count linked to the 2013 protests in February 2020. But he was detained before he had a chance to return home and then charged with the coup attempt the same night.

Prosecutor Edip Sahiner has said Kavala and co-accused architect Mucella Yapici should be convicted for attempting to overthrow the government through violence, which would carry a sentence of up to life in prison without parole.

Kavala has denied the charges.

A guilty verdict could see Kavala jailed for life without the possibility of parole.

A verdict had been expected on Friday, but the court postponed its decision until Monday to give time for defence lawyers to finish their statements.

Erdogan has made no secret of his personal enmity for Kavala, calling him a communist agent of the Hungarian-born US philanthropist George Soros who is allegedly using foreign money to try and topple the Turkish state.

“We can never be together with people like Kavala,” Erdogan declared in 2020.

The case has strained Ankara’s ties with Western allies.

Human rights advocates say that if Kavala were to be released by the court, it would send a signal to Turkey’s Western allies that its justice system is free from Erdogan’s pressure.

“His unconditional release may mark a turning point in de-politicisation of judicial prosecutions in Turkey,” Amnesty International’s Turkey researcher Guney Yildiz said.

“That’s why the result of the emblematic case is quite serious.”