If I were a betting man, I'd put my money on Poland. The Polish prime minister immediately called "sabotage" and fingered Russia, while everyone else is still saying "it could be sabotage but we need to investigate first". Russia wants the taps capable of being turned ON at their discretion, not permanently broken. This hurts their bargaining position in a big way because they've just lost their biggest source of lev…
Or, Russia realizes that Nord Stream leverage isn’t working and is now moving to attacks which implicitly threaten other pipelines (e.g., Baltic Pipe) for a stick to replace the apparently useless carrot.
That is, the next obvious offensive move is for Russia to start sabotaging more of allied Europe's energy infrastructure, increase the pain proactively. Pipelines coming out of Norway are clear targets.
Putin is an adult child throwing a tantrum because he's losing badly, being humiliated, and being shown to be weak and not brilliant. His position entirely rested on a wrong perception (that he was a highly competent authoritarian), which is now being displayed very publicly globally.