Swedish officials said Wednesday that they have decided to close their investigation into the September 2022 explosions on the Nord Stream gas pipelines which were built to carry Russian natural gas to Germany, saying they don’t have jurisdiction, Ednews reports referring to AP.

Sweden’s investigation was only one of three into the explosions. Denmark and Germany are also examining the blasts.

The attack, which happened as Europe attempted to wean itself off Russian energy sources following the Kremlin’s full-scale invasion of Ukraine, contributed to tensions that followed the start of the war. The source of the sabotage has been a major international mystery.

Russian President Vladimir Putin and Russian officials have accused the U.S. of staging the explosions, which they have described as a terror attack. The U.S. has denied involvement.

In March 2023, German media reported that a pro-Ukraine group was involved in the sabotage using a vessel and setting off from the German port of Rostock. Ukraine rejected suggestions it might have ordered the attack and German officials voiced caution over the accusation.

The German and the Danish investigation have yet to shed light on the incident and while Swedish prosecutors have said that a state actor was the most likely culprit, they cautioned that the identity of the perpetrator was still unclear and hinted that it was likely to remain so.