Pro-government news outlets have run articles suggesting that Mr. Dmitriev’s grim discovery of masses of decaying bones could have been the site of executions of Soviet Army soldiers by Finns during the so-called Winter War with Finland that began in 1939, though most historians say that is unlikely. Mr. Dmitriev’s research was not on trial but formed a backdrop for his case.
Mr. Dmitriev was arrested in December 2016 on the child pornography charges after taking nine nude photographs of his adoptive daughter, who was 11 at the time. He denied the images were pornographic.
He said he took the photos to prove that he was not beating the girl, in case social services accused him of child abuse as the official pressure against him mounted. A court-appointed committee eventually agreed that the pictures were not pornographic in nature.
The verdict on Thursday, handed down by a court in the city of Petrozavodsk, cleared Mr. Dmitriev of the pornography accusations but convicted him on a lesser charge of illegally possessing parts for a shotgun. He was sentenced to three months of probation and community service, Russian news agencies reported.
Mr. Dmitriev had also denied the firearms charge, and it was not immediately clear whether he would appeal.
Russian human rights groups had spoken out in defense of Mr. Dmitriev, saying investigators had illegally searched his house, opened a criminal case based on an anonymous claim and subjected him to a forced psychological examination, all practices reminiscent of the Stalinist past that Mr. Dmitriev had dedicated his life to exposing.