A European arrest warrant was issued for a Ukrainian man suspected of involvement in blowing up the Nord Stream pipeline nearly two years ago, Polish prosecutors said on Wednesday.

The sabotage in September 2022 of the Nord Stream pipelines that carried Russian gas to Europe has become one of the central mysteries of the war in Ukraine, prompting extensive finger-pointing and guesswork. But until Wednesday, there were very few answers.

The Polish prosecutors office said it had received the warrant, issued by Germany, in June for a suspect who was living in Poland at the time. The suspect — identified only as Volodymyr Z., in keeping with German privacy laws — left the country before Polish authorities could detain him, according to Anna Adamiak, a spokeswoman for the prosecutor’s office in Warsaw.

The German federal prosecutor’s office declined to comment on the warrant, whose existence was first reported by a trio of German news outlets.

The warrant marks the first significant development toward potentially solving who was behind an act of sabotage that has sown political distrust among Western allies and raised the geopolitical stakes in Europe’s Baltic region.

The sabotage was first detected on Sept. 26 when a vast swirl of bubbles appeared on the surface of the Baltic Sea in international waters between Denmark and Sweden.