Serhii K looked like a man without a care in the world as he checked into a glamping resort near Italy's Adriatic coast with his wife and young children. Shorts, sandals, dark baseball cap, casual banter with the receptionist, repeated raids on the free snack bowl. What could possibly go wrong?
Well, the German police, for starters. After a painstaking investigation, they had concluded that Serhii K had commanded Europe's biggest act of sabotage in decades: the September 2022 explosions deep beneath the Baltic Sea that tore through the Nord Stream pipelines and cut off Russian gas to Germany.
Next week, following his extradition to Germany and months in isolation in a high-security prison, Serhii K goes on trial in Hamburg. He is charged with causing an explosion and a war crime - attacking civilian infrastructure - allegedly on behalf of "state agencies of Ukraine". Both he and Ukraine deny any involvement. Under German privacy rules, he will be named in court only as Serhii K, but during extradition proceedings he was identified as Serhii Kuznetsov.
It was 02:03 am on 26 September 2022 when the first blast severed part of the Nord Stream pipelines, sending vast quantities of gas gushing to the surface of the Baltic Sea. Two further explosions targeted both Nord Stream 2 - not yet operational but already full - and the original Nord Stream 1, which had supplied around half of Germany's annual natural gas demand.
Prosecutors say "high-performance explosives" were planted roughly 80m (260ft) below the surface: four devices weighing up to 27kg each, activated by timers. They "strongly suspect" Serhii K led a crew that included four deep-sea divers, using a rented yacht called Andromeda. Once the complex, dangerous mission was done, the saboteurs slipped back into Ukraine, apparently unaware of the DNA evidence some had left on the boat.
As news of the blasts spread, experts and some governments rushed to the same conclusion: blame Moscow. Russia had a history of hybrid attacks and of using energy supplies as political leverage, after all. But as the airwaves filled with commentators citing "suspicious" Russian naval activity near the blast site, German police ignored the noise and followed the forensic crumbs instead.
The case built by investigators alleges that Serhii K entered Germany for the attack on a forged passport, likely issued by Ukraine's security services. In extradition files sent to Italy, he is named as Serhii Kulinich. That might explain why he looked so calm on holiday. He had been travelling widely and without incident for the past year. In a copy of his real passport seen by the BBC, there are more than two dozen stamps from countries including France, Spain and Canada - all dated after the Nord Stream attacks.
But by 13 August 2025, Germany had identified its key suspect, and this time, when Serhii K crossed into Poland, he was detected. Italian police say the actual arrest warrant was only issued on 18 August, after he had travelled south and left Poland, suggesting the Germans weren't sure their neighbours would cooperate and detain him. By the time his wife booked at La Pescaccia, he was officially a wanted man. As soon as he showed his passport at check-in, the local carabinieri got an automatic alert. Police arrived late that night and led Serhii K away from the glamping site and his family in handcuffs.
None of the Nord Stream suspects have spoken publicly, and no one admits any role in the explosions. But I have talked to some of the Ukrainians caught up in the case, and people close to them. "Anyone who admits involvement in this mission, they're immediately a target for Russia," one source explained. "Whoever did it can never confirm that."
Nord Stream was a major investment and worth big money to Moscow in fuel sales. But it also made Germany and others dependent, giving Russia immense leverage over Europe. That is why Ukraine, the US and Poland in particular all loathed it. Another source I spoke to was "eaten alive by anxiety" over the investigation and baffled that Germany, a close ally of Ukraine, was even pursuing prosecution. "Many Ukrainians believe that these pipelines helped Russia to fight, so blowing them up was a good thing for our country," they pointed out.
The German prosecutor's office told me the justice system was outside of any politics. Sabotage is an offence against Germany's constitution. Equally frustrating for the Ukrainians I met was their own government's silence. "At the very minimum, he's a military man, so if there are any questions, they should be addressed to the state, not to him," a close contact of Serhii K complained. Ahead of his extradition to Germany, his lawyer in Italy told me his client had felt "abandoned".
Germany has a whole list of suspects, but only one other name has been revealed so far. Volodymyr Zhuravlyov is currently fighting extradition from Croatia, where he was arrested in August. He was there as a consultant on a new thriller film about the Nord Stream blasts, though he denies any role in the real-life operation. Travelling was a risky move when he knew Germany was pursuing him.
Zhuravlyov has lived in Warsaw with his family since just before Russia's full-scale invasion of Ukraine and has his own business there installing air conditioning. He is also a keen and competent deep-sea diver. Last year, he was arrested in Warsaw on a warrant issued by Germany, but a Polish judge refused to extradite him. In a dramatic twist, the judge ruled that a Ukrainian attack on Nord Stream, if that was what happened, would be a "just" act in a "bloody and genocidal war". As one source close to the case put it: "The Poles don't like Ukrainians, historically, but they hate Russians and Germans even more."
The implications of this case reach far beyond the courthouse in Hamburg. After a slow start, Germany is now Ukraine's biggest supplier of military aid. The far-right AfD party, currently riding high in the polls, has seized on the Nord Stream case to bolster its argument that support for Kyiv needs to stop. It is awkward, at the very least, for the governments in both Berlin and Kyiv.
It also raises questions about what constitutes a legitimate military target: who can hit what, and where, outside an open war zone. When asked about the explosions, President Zelensky has previously insisted that Ukraine "definitely didn't do that". This week, a foreign ministry spokesman went further. "I find it very unfortunate that this entire discussion has come to focus on who blew [the pipelines] up, rather than who built them," Heorhii Tykhyi told the BBC, forcefully. He argued that the Nord Stream pipelines had "untied Russia's hands" to go to war, because it no longer needed to transit Ukraine for its gas to reach Europe. "Did we warn about this? We did," Tykhyi wanted to know. "Did anyone listen to us? No, no-one did."
Serhii K will shortly become the first suspect to face charges in this high-profile trial. Zhuravlyov's case could be merged later, in theory, though that would be complicated. Those who know Serhii K call him a patriot. He signed up to defend Ukraine when Russia invaded even though he had several children and was exempt - and fought until December 2023. His military ID shows he was still in active service when the pipelines were blown up, meaning someone in Ukraine's military command knew exactly where he was and what he was doing. And in court, Serhii K himself will not say a word, either. His legal team will argue that he is not authorised to reveal details of any activities as a soldier and produce sworn statements from two of his military superiors to back that up. I am told one of them will be the man widely named as the mastermind of the entire Nord Stream plot.