To give you one credible motive for Russian involvement: Russia cut off Europe of Gas supplies to get leverage on the Ukraine conflict, but this largely failed as European countries pooled their gas reserves and vowed to move away from Russian gas. As Russia could see that this market was lost the explosions were a last punch to send gas prices higher before the European winter and protect Gazprom from lawsuits. The mild weather killed that first motive, let's see about the other.
In September it was already clear that a weak polar vortex would make for a frosty winter in the northern hemisphere. It was just luck (for Europe) that it hit North America and not Europe. During summer in Germany every week more people were drumming up (literally) demands to open Nord Stream 2.
There was no way of being sure a German government wouldn't flip under pressure once people were freezing and showing up with torches at the Reichstag.
But one September night someone went in and shot the hostages...