Has there been any evidence released to the public that shows how and why the Russians are being attributed to the SolarWinds hack? I’ve looked at the source c

Has there been any evidence released to the public that shows how and why the Russians are being attributed to the SolarWinds hack? I’ve looked at the source code that Microsoft and others have realeased of the initial backdoor but I don’t see anything in those few lines that can positively attribute to anyone. In fact, the only thing that looked familiar was the crypto that was used to create the sub domains on the fly that hid the victims Fingerprints looked similar to what has been used in mobile malware created by China but that is still too flimsy to attribute anyone to as well.