Gulag historian Yuri Dmitriev has today been handed a three-and-a-half-year jail term, his lawyer confirmed.
The sentence was for "violence of a sexual nature" against his adopted daughter.
But his supporters say the case is an attempt to silence Dmitriev, who has spent nearly 30 years compiling a list of the 40,000 people deported or executed under Joseph Stalin in Karelia, a Russian region bordering Finland.
Dmitriev, 64, was first arrested in 2016 on accusations he had produced "pornographic" images of his adopted daughter.
He was acquitted in 2018 but the Supreme Court of Karelia overturned this decision two months later and ordered a second trial, this time for "sexual violence against a minor".
"Dmitriev himself does not admit any of the accusations," said the human rights NGO Memorial before the verdict. "Memorial is sure of his complete innocence.
"The obvious reason for the historian's persecution is his many years of work to find the burial places of people killed during the Great Terror, to establish lists of victims, to preserve memory in places of Stalin's executions."
In recent years, Dmitriev has also been behind the discovery of one of the largest mass graves in Karelia, at Sandarmokh, where the remains of 7,000 to 9,000 people executed during the Stalinist era have been found.
Numerous Russian and international figures have denounced unjustified prosecutions against Yuri Dmitriev. At a press conference in early July, director Alexandre Sokourov said the historian's conviction would constitute "a turning point" in Russia.
Meanwhile, Nobel Prize winners, Belarusian writers Svetlana Alexievitch and German Herta Müller have asked the Council of Europe, a pan-European organization of 47 states, to react. They believe that Dmitriev's findings in Sandarmokh were a "bone in the throat of the authorities" who, according to the two authors, seek to "rewrite history".