I'm going to go with the journalist who has a long history of exposing US atrocities on this one. It's incredible not to presume that the party with the history, the motive, and the means to carry out this kind of a terrorist act carried it out. Especially given that top US officials said the pipelines would be stopped and then all but bragged about this after they were destroyed.

It's also hard to carry out any kind of a proper investigation when one of the parties whose pipeline was blown up is prevented from investigating. The pipeline was owned by Russia, and the west is not allowing Russia to investigate what happened. This precludes any kind of proper investigation, and indicates that there is something western countries want to hide.