Serhii K was detained by German police at a glamping resort near Italy's Adriatic coast, where he had arrived with his wife and young children. Investigators concluded he commanded what they describe as Europe's biggest act of sabotage in decades: a series of explosions that ripped through the giant Nord Stream pipelines and severed the supply of Russian gas to Germany. Three of the four Nord Stream pipelines were ruptured in the blasts.
He faces charges of causing an explosion and of committing a war crime by attacking civilian infrastructure, allegedly on behalf of "state agencies of Ukraine". Following his extradition to Germany, he spent months in isolation in a high-security prison.
Under German privacy rules he will be named during the trial only as Serhii K, but he was identified as Serhii Kuznetsov during extradition proceedings. Both he and his country have denied any involvement in the attack.
The trial opens next week in Hamburg.