Propaganda says both: first that Russia did it, then that Ukraine did it. The former is insulting stupid and the second is more subtle but still makes no logistical sense, as Ukraine lacks the specialized equipment and personnel required. The "Ukraine did it" narrative is one that's still safer for the NATO bloc group that certainly did it, as even if they acknowledge it as true (which they don't need to and have avoided doing), it's easy to brush under the rug as Good Slava Ukraini Resistance.

This is why these countries doing investigations are mum. They know neither narrative is true.