Why would russia do this?
They gain absolutely nothing from it and lose everything. They lose all the levrage over germany they had. Russia controls the flow of the gas. They could turn if on and off as they please to get germany to play ball. And there were protests about this in germany, i do not think we couldve continued to support ukraine with the energy shortage given that russian gas wouldve been an option if we just stopped opposing russia, now it isnt, now there is no reason at all to negotiate with russia.

There are many canidates who couldve done it, russia i think can pretty much ruled out, they dont have any motive (unless as a false flag but that wouldnt work, the world thinks they did it anyways) nor access to that part of the ocean.

If it was the new baltic pipe that was blown up - which, whoever did this couldve done, it crosses nordstream not far from one of the bombingsites - well that wouldve made sense.
This baltic pipe conveniently started operating one day before this happened by the way.
Which puts norway, denmark and poland on the list so to speak.
Poland would make a lot of sense - and a polish chairman of the US-EU delegation immediately credited the USA.