The sabotage of two undersea gas pipelines in 2022 remains a mystery as Sweden ended a probe without reaching any clear conclusions on the identity of the perpetrators.

The preliminary investigation was dropped given nothing indicates that the attack involved Sweden or its citizens, the prosecutor’s office said in a statement on Wednesday.

While speculation has been rife about who caused the underwater explosions that ruptured the Baltic Sea pipelines in September 2022, investigators have now concluded that Swedish authorities have no jurisdiction over the case and are unable to take the probe further.

The undersea link to Germany was the main route for Russian pipeline gas flows before the Kremlin’s invasion of Ukraine. In 2021, the year before the war started, it delivered more than a third of Russia’s total gas exports to Europe.

Europe is still recovering from the sector-wide energy crisis caused by the cut off of supplies after the attack. Germany was one of the hardest hit nations and was forced to take one of its major gas suppliers into state hands as it urged citizens to use conserve fuel. Countries across the region drew up emergency plans for keeping critical services going in case of shortages.

An investigation into the incident remains pending in Germany, the country’s Federal Prosecutor’s Office said in an emailed statement on Tuesday, declining to provide more details.

“We have cooperated closely with the preliminary investigation that German authorities are conducting,” Mats Ljungqvist, the prosecutor who led the Swedish probe, said in a statement. “Within the framework of that cooperation we have handed over material that can be used as evidence in the German investigation.”

Russia is interested in “how scrupulously” German authorities will approach the investigation given Germany “has lost a lot due to this terrorist attack,” Kremlin spokesman Dmitry Peskov told reporters on Wednesday, when asked about Sweden’s decision, according to Interfax.

The German government is “still very interested in the solution of this crime,” Steffen Hebestreit, the spokesman of Chancellor Olaf Scholz, told reporters in Berlin on Wednesday. He declined to comment on Peskov’s remarks, but added that the government has taken notice of the Swedish decision, without giving details.

Earlier media reports have indicated that authorities had identified and searched a yacht believed to have been used by the attackers.

The explosions in 2022 damaged both strings of the Nord Stream 1 pipeline that at peak capacity delivered 55 billion cubic meters of natural gas annually, as well as one of two strings of Nord Stream 2. The second pipeline was set to double capacity but never entered service.

Russia is ready to supply gas via the remaining string of Nord Stream 2, but the German government will have to allow that, President Vladimir Putin said in October. Russia has repeatedly called the incident an international act of terrorism.

The Nord Stream blasts demonstrated the vulnerability of seabed infrastructure and prompted an increased military presence in the Baltic Sea. 

Covert underwater activity is notoriously hard to prevent as well as attribute, and in October last year, a gas pipeline connecting Estonia and Finland was ruptured by a ship dragging its anchor along the sea floor. It remains unclear whether the Hong Kong-flagged container ship deliberately sabotaged the pipeline, and Finnish authorities are working with Chinese officials to probe the matter.