Who did it and why?
That would be Poland.
https://www.euronews.com/2022/09/27/baltic-pipe-norway-poland-gas-pipeline-opens-in-key-move-to-cut-dependency-on-russia
>The pipeline will transport natural gas from the Norwegian shelf via Denmark and through the Baltic Sea to Poland. It is the centrepiece of a Polish strategy to diversify away from Russia that began years before Moscow’s February invasion of Ukraine triggered a global energy crisis.
>The flows from Norway along with supplies via liquefied gas terminals are central to Poland's plan. The country was cut off from Russian gas supplies in April, allegedly for refusing to pay in roubles.
>"The era of Russian domination in the field of gas is coming to an end, the era that was marked by blackmail, threats and extortion," Polish Prime Minister Mateusz Morawiecki said at the inauguration at Budno in western Poland.
https://www.euronews.com/my-europe/2022/09/27/denmark-and-sweden-issue-navigation-warnings-over-nord-stream-gas-leaks
>"Today we faced an act of sabotage, we don’t know all the details of what happened, but we see clearly that it’s an act of sabotage, related to the next step of escalation of the situation in Ukraine," said Polish PM Mateusz Morawiecki
Can Poland do that even theoretically? I mean, the area is monitored by Dane and Swedish navy & coastguard, there was some US navy presense and some Russian monitoring from the sky and the sea depth is monitored by satellites as well. It would require some crazy tech to do that right under their noses, do Poles have something like that?
> pass over the gasline and drop
So you need to pass straight over it but people can simply track down which ships passed there in latest hours. Is this place along some busy trade routes?
But American satellites detected these submarines even back during the cold war and now I believe their tracking quality improved. Are you supposing some secret soviet stealth submarines that were never disclosed are still stationed there?
Couldn't they just stop paying and say "I don't wanna pay cause you're bad Nazi people" or something?
To me the whole situation is pointless, nobody gains from it more than loses. I think it's either some provocation and we're yet to see where it goes or some stupid mistake and nobody actually wanted to explode it right now.
Dumb contractual obligations. In case you haven't noticed, countries were dropped from gaz whenever their current contract was up and they didn't want to sign a new one in rubles.
Bulgaria's contract was up quite early, so they were unplugged early, despite them being among the more friendly countries to Russia in Europe.
https://www.rt.com/news/554575-bulgaria-russian-gas-stop/