By Ali Kucukgocmen and Ece Toksabay
ISTANBUL (Reuters) -Turkish opposition leaders vowed to overturn jail sentences against philanthropist Osman Kavala and seven others convicted at the end of a case that lawyers said showed courts had become the government's "vehicle for revenge".
Kavala was sentenced to life in prison without parole, while seven others got 18 years based on claims they organised and financed nationwide protests in 2013, charges from which they were acquitted two years ago.
The verdict was seen as symbolic of a crackdown on dissent under President Tayyip Erdogan and the punishment of the government's perceived foes through the use of the judiciary.
Kemal Kilicdaroglu, leader of the Republican People's Party (CHP), promised on Monday to reinstate the rule of law if the opposition wins elections scheduled for June 2023.
"In this fictitious trial, Osman Kavala was sentenced to life in prison in a case in which he was previously acquitted," he said in a speech to CHP members on Tuesday.
"We will fight against those who place the judiciary under the orders of politics.... and hold our people hostage in prisons," said Kilicdaroglu, who is seen as Erdogan's likely challenger for the presidency.
His description of the so-called Gezi protests as "a national movement" stands in contrast to Erdogan's view that the demonstrations aimed to topple the government.
Hundreds of thousands marched in Istanbul and elsewhere in Turkey in 2013 as demonstrations against plans to build a replica Ottoman barracks in the city's Gezi Park grew into nationwide protests against Erdogan's government.
The president has equated the protesters to Kurdish militants and those accused of orchestrating a failed coup in 2016. He has accused Kavala personally several times of being the financier of the protests.
But the CHP and five other opposition parties that have formed an alliance to defeat Erdogan in the next elections have sounded the alarm over the verdict.
"The members of the judiciary, who conduct the trial themselves, have abandoned their authority and ability for judgement," said IYI Party general secretary Ugur Poyraz.
More than 1,000 people gathered on a narrow street near Taksim Square to protest against the verdict on Tuesday, chanting "freedom to political prisoners" among other slogans. The Istanbul governor's office said 51 people were detained.
Lawyers earlier staged a protest in Istanbul's main courthouse, and some 300 people also gathered in central Ankara.
Ankara's Western allies, opposition members and rights groups say Turkish courts are under the control of the government. Erdogan and his AK Party say they are independent.
The investigation that began with Kavala's detention in October 2017 has seen various turns that cast doubt over the legality of the judicial process, which critics said aimed to "rewrite history" and criminalise the Gezi protests.
The indictment in the case alleged links between George Soros and Kavala, in what lawyers said was an attempt to create the perception that the protests were funded by foreign powers.
The indictment said the fact that defendants discussed bringing milk, juice and pastries to Gezi Park, as well as gas masks to counter the effects of tear gas, showed they were financing the protests.
Another court ruled in 2020 that the evidence, initially gathered by a group within the judiciary that Ankara accuses of orchestrating the coup, was not enough for a conviction.
Similar concerns were highlighted by one of the judges who dissented from Monday's verdict.
The judge, one of three presiding, said the only evidence was phone taps that were collected illegally and, even if they were legal, were not enough to convict by themselves.
All defendants should be acquitted and Kavala, who had been in prison for 4-1/2 years without a conviction, should be released, the judge wrote in his dissenting opinion.
Veysel Ok, lawyer and co-director of Media and Law Studies Association, said Monday's verdict was void of "judicial logic" and aimed to intimidate those seeking the rule of law.
"This ruling shows us the picture of a judiciary that has become a vehicle for revenge due to political interests. It is a sign that no one in Turkey has legal security," he said. The verdict showed the judiciary would be used "as the fundamental weapon" to "bring the opposition to line" before the elections.
"It indicates that a much harsher period awaits us and that the public opposition and civil society need to stick together."
The European Court of Human Rights (ECHR) called in Dec. 2019 for Kavala's release, saying his detention served the purpose of silencing him.
But Kavala's continued detention means Turkey faces being suspended from the Council of Europe rights watchdog, after it launched rare infringement proceedings against Ankara.
Kavala was re-arrested hours after the acquittal and has remained in jail for the last two years on an espionage charge, a move seen as attempting to circumvent the ECHR ruling. Kavala was acquitted of espionage on Monday.
All defendants have always denied the charges, saying the Gezi protests were protected by constitutional rights.
Three defendants, Mucella Yapici, Can Atalay and Tayfun Kahraman, said jointly in court on Friday that the Gezi protests were not organised by a group but erupted spontaneously.
"The Gezi resistance is the most democratic, creative, egalitarian, comprehensive and peaceful mass movement in the history of this country," they told the court.
"The only force that can lead millions of people to spill on to the street for weeks can only be people's own will."
(Writing by Ece Toksabay; Editing by William Maclean and Barbara Lewis)