When the police banged on his door and took him away for questioning one dawn in November 2018, Yigit Aksakoglu assumed he would be home in time to catch his afternoon swim.

But after a 10-hour interrogation, he was hauled off to court and thrown into jail in solitary confinement for seven months on a charge that is among Turkey’s most heinous crimes, violently attempting to overthrow the government.

The Turkish representative for a Dutch charitable foundation specializing in programs for the social development of young children, Mr. Aksakoglu, 43, never expected to run into trouble with the law. Even when President Recep Tayyip Erdogan of Turkey began mass arrests after a failed coup in 2016, sweeping up many innocent academics, journalists and human rights activists, he never thought he would be caught up in it, too.

“I was picked accidentally,” Mr. Aksakoglu said in an interview at his office in central Istanbul. “And now they are unable to unpick me.”

A verdict in his trial is expected on Tuesday and he, along with 15 co-defendants, faces a possible sentence of life without parole. “Just like a lottery I will probably spend a long time in prison,” he said.

The prosecutor has called for the harsh sentence despite Mr. Aksakoglu’s insistence that the charges are baseless and the evidence flimsy. Fears are mounting that under Mr. Erdogan’s increasingly autocratic rule, he and his co-defendants will be punished in order to send a chill through Turkey‘s dwindling community of independent organizations and activists.

“The 18th of February will be the funeral of civil society in Turkey,” Mr. Aksakoglu said. “No one will be willing to raise even a tiny voice.”

The case stems from the Taksim Square protests of 2013, when students, artists and environmentalists opposed the construction of a shopping mall in one of Istanbul’s central parks. The trial is being watched closely by Western diplomats who want to see an improvement in Mr. Erdogan’s record on human rights and the rule of law.