In brief: As hearings resume in Hamburg this week, investigators will turn to the yacht allegedly used in the sabotage. Interviews with the defense and legal scholar Kai Ambos reveal the arguments that could shape the case against Serhii Kuznetsov.
At the heart of the Nord Stream trial are questions that reach beyond the reconstruction of an act of sabotage to the limits of lawful warfare and individual criminal responsibility.
Could the pipelines qualify as military targets, and could acting for a state offer protection from prosecution? Ukrainian secrecy obligations already constrain Serhii Kuznetsov’s defense, his lawyers say. If prosecutors establish his involvement, what he understood about the mission and any orders he received could become decisive.
It is Oct. 27, the second day of the Nord Stream trial. In Courtroom 237 of Hamburg’s criminal courthouse, Serhii Kuznetsov, the Ukrainian accused of coordinating the September 2022 pipeline sabotage, sits between his two lawyers, listening to an interpreter through headphones, his demeanor composed and attentive.
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Under tight security, journalists and members of the public follow the hearing from behind Plexiglas panels. From their seats, a slightly open window offers a view of Hamburg’s remand prison, where Kuznetsov spends his days in what his lawyers describe as effective solitary confinement.
“He is alone for 23 hours on a wing where he has no contact with others,” Lars Brögeler, one of his lawyers, told Kyiv Post.
Even his exercise period is spent alone. His family remains in Kyiv, adding another strain to the isolation: each morning, Brögeler said, his client wakes wondering whether they are still alive.
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Opposite Kuznetsov is Stefan Schmidt, representing Germany’s federal prosecution service.
“The alleged impediment to the proceedings does not exist,” Schmidt told the court in his submission ahead of the ruling. Any refusal to release Kuznetsov from Ukrainian secrecy obligations, he argued, falls within Ukraine’s responsibility, not Germany’s.
Bound by secrecy
“Under German law, the defendant is not restricted in his defense,” presiding judge Anne Meier-Göring said, explaining the rejection of the defense’s application.
The reasoning turns to who imposes the restrictions and who brings the prosecution. Court spokeswoman Marayke Frantzen explained that a different problem would arise if Germany itself required a defendant to keep information secret while prosecuting them over matters they are consequently unable to discuss in their defense.
Court spokeswoman Marayke Frantzen inside Hamburg’s criminal courthouse on Oct. 27, 2026. Photo by Korbinian Leo Kramer.
Here, however, the alleged secrecy obligation comes from Ukraine.
“The service regulations of another state cannot bind us in Germany,” she said, explaining the senate’s position.
That distinction leaves a practical question: What might happen to Kuznetsov in Ukraine if he chose to speak?
“The senate did not actually address in its decision what consequences such conduct would have for him in Ukraine,” Frantzen said.
The judges therefore did not need to establish whether the claimed Ukrainian secrecy obligation actually exists: Even if it does, they do not consider it a bar to prosecution in Germany.
Even when an application fails, the court’s explanation can help shape the defense’s next move.
Yet the difficulties raised by the defense are not simply being dismissed. Frantzen indicated that Kuznetsov’s detention conditions could be eased, while the constraints on his defense will also matter when the judges weigh the evidence. If Kuznetsov continues to remain silent against this background, it falls to the judges to approach the other evidence “particularly critically” and keep those circumstances in mind.
“It was fairly predictable that the proceedings would not end on the second day,” said Kuznetsov’s other lawyer, Jes Meyer-Lohkamp. “The point was to make people understand: Why isn’t this man speaking? What is behind it?”
“We are not persuaded by the outcome. The reasoning, though, is interesting,” his colleague Brögeler said. He describes the exchange as a “formalized dialogue”: Even when an application fails, the court’s explanation can help shape the defense’s next move.
The lawyers nevertheless face a practical difficulty: Their client invokes secrecy obligations that, they said, prevent him from sharing information even with his own counsel.
“Unlike the court and the federal prosecution service, we take this seriously,” Brögeler said.
Jes Meyer-Lohkamp (left) and Lars Brögeler, who represent Serhii Kuznetsov, outside Hamburg’s Hanseatic Higher Regional Court on Oct. 27, 2026. The trial takes place in the neighboring criminal courthouse, which has a courtroom equipped for heightened security requirements. Photo by Korbinian Leo Kramer.
A legitimate target?
Alongside the dispute over his alleged involvement runs a separate question: What role did the pipelines play in 2022 in Russia’s ongoing war against Ukraine?
“Of course, this is an intensely political trial,” Brögeler said. “What was Putin really using them for?”
His argument reaches beyond the revenue Russia earned from gas exports to Moscow’s use of energy supplies to influence European governments. Brögeler disputed the prosecution’s description of the pipelines as purely civilian supply infrastructure.
“We say no: Its purpose was not unambiguously civilian. That purpose changed completely in 2021-22. Gas was used as a weapon to pressure European countries into reversing sanctions,” he said.
The difficulty lies in how far the definition of a military target can be stretched beyond such clear-cut cases.
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For Kai Ambos, a professor of criminal and international law at the University of Göttingen, the implications of that argument extend well beyond Nord Stream. Classifying the pipelines as a military target on such grounds, he argued, risks weakening the principles used to condemn Russian attacks on Ukraine’s civilian infrastructure.
The question is how far opposing sides could stretch that justification to defend their own attacks.
“In the end, every Russian taxpayer is contributing to the Russian war effort,” Ambos said. If generating revenue for a belligerent state were enough to make something a military target, the same argument could extend from energy infrastructure to businesses and ultimately to the people paying those taxes.
“It’s obvious that you can attack a Russian tank. It’s obvious that you can attack Russian shooting stations in Russia,” Ambos added.
The difficulty lies in how far the definition of a military target can be stretched beyond such clear-cut cases.
Kai Ambos, professor of criminal and international law at the University of Göttingen, speaks from his office during a video interview with Korbinian Leo Kramer. Screenshot by Korbinian Leo Kramer.
The same rules for both sides
“This law is not a law for enemies and friends. It’s the same law applicable to everybody,” he said.
Ukraine, he said, is bound by the Geneva Conventions and their Additional Protocols just as Russia is. Its right to defend itself does not remove the limits on what it may attack.
According to Ambos, treating Nord Stream as a military objective because of its broader contribution to Russia’s war effort would therefore require accepting the same reasoning when assessing Russian strikes on Ukrainian facilities.
The international law scholar cited Putin’s use of Western arguments about Kosovo in relation to Ukraine to show how justifications travel beyond the circumstances in which they were first advanced.
“If you allow to bomb infrastructure for civilian population, you are opening the floodgates.”
“We have given him arguments, and we should stop. We must be consistent here,” he said.
There are nevertheless substantial differences in the consequences of the attacks. When challenged on the contrast between Germany, where the pipeline explosions did not leave households freezing, and Ukraine, where Russian strikes repeatedly deprive civilians of heat and electricity, Ambos returned to the purpose of the protection itself.
Germany’s ability to secure alternative energy supplies does not, in his view, settle whether an attack is permissible.
“If you allow to bomb infrastructure for civilian population, you are opening the floodgates,” he said.
His concern extends to other conflict zones, including Sudan, Gaza, Lebanon and Iran: an interpretation adopted in one conflict can become a justification in another, with civilians bearing the consequences.
That position leaves him personally uneasy about the prosecution of a Ukrainian accused of acting against Russia.
“As a political person, I don’t like this at all. But I have to talk to you as a lawyer,” he added.
“I’m absolutely in favor of the Ukrainian fight against Russia,” he said, but that support does not alter his underlying conviction.
“We have to have strict rules for the sake of all of us as being civilians.”
The defense’s remaining options
Looking back to the start of the investigation, Ambos sees a missed opportunity for political intervention. The federal justice ministry, he argued, could have instructed federal prosecutors not to pursue the case.
“But that’s over now,” he said.
The distinction between civilian and military targets has already been examined by Germany’s Federal Court of Justice (Bundesgerichtshof, or BGH), with consequences that Ambos believes will shape the defense’s prospects in Hamburg.
“Strategically, the defense made a big mistake by challenging the pre-trial detention, bringing the case before the Federal Court of Justice, which turned it into a war crimes case.”
A soldier trained for the operation might therefore understand his actions differently from the judges assessing them later.
In their decision of Dec. 10, 2025, the judges of the BGH’s Third Criminal Senate classified the pipelines as civilian objects and rejected the claimed wartime justification, while also denying functional immunity for intelligence-directed violence infringing another state’s sovereignty.
The immunity argument rests on the claim that Kuznetsov acted for Ukraine as a military officer, invoking protection from foreign prosecution for acts performed on a state’s behalf. With the BGH’s ruling already in place, Ambos expects little room for a different outcome in Hamburg.
“I see no way that he will get immunity,” he said.
Ukraine’s own position complicates the argument further.
In its submission to the UN’s International Law Commission, Kyiv endorses the exclusion of functional immunity for war crimes, crimes against humanity and genocide, and argues that the crime of aggression should be included as well. Seeking an exception for a Ukrainian accused of such an offense, he argued, “would be a double standard.”
An unlawful act, an innocent mistake?
Ambos sees a more promising line of defense in separating the attack’s legality from Kuznetsov’s personal culpability. If his involvement is established, could he have believed he was carrying out a lawful operation in defense of Ukraine?