[August]

I think the fact that one of the four pipelines was left untouched, not damaged or even prepped to explode, but deliberately ignored, points the deed to Russia.

If it were Ukraine or the Poles or the US, then all four pipes would have been destroyed and if one of the charges had failed it would have left behind evidence or damage but none exists. We would not have left the option open for Russia to turn the spigot back on someday. Only Russia has the motive to keep one of the pipes intact.