Lots of speculation over the “Who” but none of the proffered theories and speculation really fit.
But an interesting theory has come to light – laying the blame on incompetence rather than malice.
https://thelawdogfiles.com/2022/09/nordstream.html
I suspect someone in the Russian government pinged Gazprom, and said, “The EU is about to have a cold winter. make sure those pipelines sodding well work, so we can sell someone natural gas at massively increased prices.”So, Somebody In Charge started running checks — and came up with hydrate slurry in both pipelines. After the running in circles, hyperventilating, and shrieking of curse-words stopped, somebody started trying to remediate both lines. Of course they didn’t tell folks down stream — no Russian want to look weak, and besides, there’s been a nasty uptick in failed Russian oligarchs getting accidentally defenestrated — they just unilaterally tried to Fix Things.
The Fixing of Things went bad. One went Paws Up, and they started trying to stop the other — but pressurisation (both ways) is a weeks-long process, and the second went bad, too.
The post goes into detail about what needed to be fixed, ( Hydrate Plug ) how it should be fixed, (Very slowly and Very carefully) and what can happen if it doesn’t get fixed properly (Boom). It’s an interesting read and the poster seems pretty confident that what happened was inevitable and not just bad luck on the day.

