Biden himself told they would do it, and "promised they have ways to do it" (from ca 1:20): https://www.youtube.com/watch?v=OS4O8rGRLf8&t=82s
Which means, since this is cloak-and-dagger stuff, we could add to the list of suspects "anyone who could get access to that Pipeline and wants to destabilize relations between the United States and Germany."
It does make it hard for Germany and Russia to have energy trade, however.
Which makes it easier for the USA to sell its dirty gas in Europe.