zlacker

The Baltic states, Poland, Ukraine, Sweden and so on, all understand that they have duties to Germany due to their EU membership and further understand that they are dependent on the German economy and that any action of this kind, which jeopardises the German economy, jeopardises also them.

Thus you cannot easily imagine any of the Baltic states, Finland or Sweden doing the deed.

Norway is conceivable-- but they're not really all that active in the Baltic sea, Ukraine is conceivable-- but it isn't actually super easy to do what was done. Blowing up the pipeline would have been easy, but there were several bombs, and they were, as I understand it, quite big, and this would be removal of resources from things closer to the fighting.

Norway is difficult for political reasons though-- would they really screw over their neighbouring countries in the EU?

Thus all these countries are all unlikely choices.