what our resident pootin apologists and tinfoil enthusiasts seem to "forget", while spreading their simplistic pro kremlin takes on the issue, is the other side of their "reward" equation:
while it's true that this benefits the interest of the shitty american lng industry, which very much has been an economic goal of several US administrations, the risk involved in blowing up those pipelines is MASSIVE for the US, and pales in comparison to whatever "benefit" (a re-orientation on the gas market, something germany was already forced to do) this results in. the baltic sea is a relatively closely monitored body of water, seismographs picked up irregularities (most likely explosions) right away. should american operatives be caught or found out to be behind this, it'd have major diplomatic and economic consequences, it'd result in a massive fallout and shatter the relations between the two countries. i think it's incredibly unlikely the US is behind this, even though i personally wouldn't rule it out entirely. they are not "good" guys.
you'd also have to be pretty dumb not to realise russia's possible motivation: have germany and the EU pressure ukraine into peace negotiations that favour russian demands. that and the general chaos and economic damage this created. the "argument" that russia would destroy its leverage by blowing up those pipelines, and therefore couldn't possibly be behind this, is plain stupid - at least if you're even remotely familiar with the situation. even prior to the sabotage, russia had made transparent "excuses" not to deliver gas to germany (the whole turbine saga in august comes to mind), they already used that bargaining chip. also, russia doesn't risk much by blowing up those pipelines. they are already diplomatically and economically isolated from the west, and they know that even if caught red handed, it's unlikely this would trigger an open war with a nuclear power.
additionally, the CIA apparently already warned the german government this summer that those pipelines could be a possible target for acts of russian sabotage. again, that does not technically rule out they're behind it, but it makes it even less likely. common sense as well as an honest evaluation of risks and rewards clearly point to russia as the culprit, no matter what the likes of ampootin and void were fed on facebook...