I think elements, using primarily NGO's... and possibly driven by NGO's (aka... foundations, billionaires, tech oligarchs), would and could do some very, very dastardly things. And did. Don't get me wrong.
But an operation on a 200M pipeline, unless someone shows me Mark Zuckerberg or Bill Gates is running special operations submarines, virtually has to come from a nation state.
You have to look at capabalities and intentions... and will! People forget Part III.
We have the capabilities. We might have the intentions. We are too 'bureaucratize' to be able to demonstrate the will.
In the East.. there are places with the capabilities. And the intentions. And the will. This has FSB/SVR and Russian .Mil all over it. Along with maskirova to blame everyone else. Don't discount the Ukrainians, either. They are sneaky bastards and heirs to the old Soviet system. As well as having a nice cozy money-laundering relationship with the people in 'Our Gummint' who you reference above. That makes for a convenient capability run through NGO's... and 'connected' individuals that does not represent government policy and did not access US resources.
Occams razor here, imho, does not say 'Accident,' But thats just my opinion. It sure as hell points a big neon flashing arrow right at the Eastern Bloc.
Just my opinion. Meh, what do I know anyway.
Sirhr