Along with Berlin and Stockholm, Copenhagen has also launched an investigation into the two blasts that destroyed three of the four strands of the Nord Stream 1 and 2 pipelines, which connected Russia’s Siberian gas fields to Germany through the Baltic Sea, in September 2022.
But the explosions remain shrouded in mystery, as investigators have so far been unable to identify a culprit.
Sweden and Denmark have labeled it a deliberate act of sabotage, and Swedish prosecutors later found traces of explosives at the site of the blasts.
German investigators, meanwhile, have traced the explosives back to a yacht which they suspect was used to transport them to the blast site.
The uncertainty around the attack has fueled a range of theories seeking to uncover who was responsible.
Several countries have been publicly blamed for the explosions, with varying degrees of evidence. Ukraine has blamed Russia for the bombing, and Poland has also hinted that Moscow was responsible, which the Kremlin has denied.