Vadim Ostanin, who had run Navalny’s local headquarters in the Siberian city of Barnaul, had carried out only “legal political work”, Navalny’s team wrote on the Telegram app.
He was also found guilty of involvement in a non-profit group “whose activity involves violence against citizens”.
Ostanin was arrested in December 2021 and held in Moscow before being transferred to Barnaul, where he stood trial.
“Upon my arrival in Barnaul from Moscow, without explanation, I was placed in a solitary cell, about six square metres, in a basement with a window covered with debris,” Ostanin wrote in a letter published by Navalny’s team.
“About a week later, the cell was flooded with ankle-deep water…In these cells there were rats, ants, spiders,” he wrote.
Navalny’s team wrote that investigators had pressured Ostanin to admit his guilt, but he refused.
Navalny, Putin’s best-known critic, is serving sentences totalling 11-1/2 years in a penal colony on fraud and other charges he says were trumped up to silence him. Last week Russian state prosecutors requested a court to jail him for another 20 years in a new criminal trial for charges including extremism.
Last month another Navalny campaigner, Liliya Chanysheva, was sentenced to 7-1/2 years for “extremism”.