Haven't the NSA already said they believe it was the Russians? As you suggest, they would be the ones to know.

The NSA doesn't, in general, publicly announce anything. They exist to supply analysis to other branches of government, and only very rarely to the public directly. So the absence of commentary from them in public doesn't indicate that they haven't drawn conclusions and passed them along.

Source? I googled it and only found articles suggested the opposite.

ex.https://theintercept.com/2016/12/29/top-secret-snowden-docum...