Swedish authorities on Wednesday concluded a more than year-long investigation into the undersea attack on the Nord Stream pipelines, citing a lack of authority to prosecute those responsible for sabotaging the crucial piece of energy infrastructure intended to power West -To supply Europe with Russian gas, to be continued.

“Sweden does not have the jurisdiction to investigate this matter further,” the Swedish Security Service said in a statement on Wednesday. The September 2022 attack over the natural gas pipelines – just seven months after Russia's massive invasion of Ukraine – led to rampant public speculation about who was to blame. Attributing responsibility for the attacks seemed urgent for Europe, while so did Russia seen as a possible perpetratorbut the case became increasingly complex over the past year intelligence suggested that the sabotage had been carried out by a pro-Ukrainian group.

The series of underwater explosions ripped holes in three of the four parts of the Nord Stream pipelines and led officials to conclude that they were most likely caused by a state actor. Some saw the attacks, which nearly damaged a cable carrying electricity from Sweden to Poland, as a warning sign that raised concerns about what other infrastructure might be vulnerable.

The explosions took place in international waters, but also in the economic zones of Sweden and Denmark, giving these countries a starting point to investigate.

The crime scene, along the bottom of the Baltic Sea, yielded little concrete evidence the Swedish authorities recognized in the early months of the investigation, even as they kept a close eye on their investigation and refused to join their investigative forces with authorities in Denmark and Germany.

On Wednesday, Swedish authorities said their investigation had been “opened to investigate whether the sabotage was directed against Sweden and thus endangered Sweden's security, and it was determined that this was not the case.”

The Swedish security service cited intensive cooperation with other international authorities and said the investigation's findings had been shared.

After the attacks, Poland and Ukraine openly blamed Russia, albeit without citing evidence. Russia in turn accused the United States, Britain and Ukraine, also without evidence.

Last year, after intelligence suggested that a pro-Ukrainian group carried out the sabotage, U.S. officials who reviewed the findings said they had no indication that Ukrainian government officials had any ties to the operation.

Subsequently, several other clues emerged that further fueled the case public speculation and competing narratives.

Mats Ljungqvist, a senior prosecutor leading the Swedish investigation, suggested to The New York Times last year that he had his own suspicions.

'Do I think it was Russia that blew up Nord Stream? I never thought that,” he said. “It doesn't make sense. But just like with a murder, you have to be open to all possibilities.”

The Central Intelligence Agency told Ukrainian officials last summer that it had learned of what it believed was a failed plot by the Ukrainians to attack the Nord Stream pipelines, and the agency strengthened its objection to such an operation.

According to US and European officials, Dutch intelligence officials shared information with the CIA in June 2022 that they had learned that the Ukrainian military had planned an operation that would deploy divers to blow up one of the pipelines. But the original tip from the Dutch, according to a US official, was that Ukraine had already reconsidered and canceled the operation.

In reality, US officials now believe, the operation was not aborted but postponed, possibly with another Ukraine-aligned group carrying out the attack.

Explosions in September destroyed parts of the pipelines that carry natural gas from Russia to Europe. The Ukrainian government denied responsibility for the attack.

But German investigators later learned that a group of Ukrainians had rented a boat, loaded it with explosives and attacked the pipeline. US intelligence agencies now believe the operation was at least carried out under the loose leadership of the Ukrainian government, but they do not know who exactly planned the operation.

The information about the CIA alert to Ukraine, and that it was Dutch intelligence officials who provided the original intelligence, was previously reported by the German news channel Die Zeit and NOS, the Dutch national broadcaster.

It is unclear which US official delivered the message about the pipeline attack in Ukraine. However, it was not delivered by senior officials because the United States already believed Kiev had reconsidered the wisdom of the attack, the US official said. It was also not clear how the Ukrainians reacted to the message from the Americans.

The original alert, collected by Dutch intelligence, contained details similar to the last operation, but also differed on several key points, the European official said. The original intelligence said Ukraine planned to attack Nord Stream 1, while the actual attack targeted both the older pipelines and the just-completed set known as Nord Stream 2.

Dutch intelligence also reported that the plan would involve the use of fake Estonian passports, the European official said. At least some members of the group believed by European investigators to have carried out the attack used false Bulgarian passports.

The original plan also included using Ukrainian special forces personnel to hire a submarine and a boat to attack the pipelines, near a spot popular with divers, the European official said.

The CIA could not confirm the information the Dutch provided last summer, but nevertheless warned the German government that the pipelines could be attacked and then discussed the matter with Ukrainian officials.