There's a fair bit of evidence in Mueller's report: https://www.justice.gov/storage/report.pdf. But probably the most damning evidence is still highly classified.

There's evidence released by private firms, including ThreatConnect, FireEye, CrowdStrike, Fidelis, and Dell SecureWorks, who have been tracking Russian intelligence groups, including the ones that they allege hacked the DNC, for many years prior:

* https://threatconnect.com/blog/reassesing-guccifer-2-0-recen...

* https://www.fireeye.com/current-threats/apt-groups/rpt-apt28...

* https://www.crowdstrike.com/blog/bears-midst-intrusion-democ...

* https://www.fidelissecurity.com/threatgeek/archive/findings-...

* https://www.secureworks.com/research/threat-group-4127-targe...

(There are varying degrees of technical details in each report, but I recommend reading them all to get a full picture.)

Dutch intelligence says they hacked GRU computers and cameras and observed the hacks as they were happening: https://arstechnica.com/information-technology/2018/01/dutch.... They contacted NSA, and this may have been the first time US intelligence became aware of this.

The evidence is so comprehensive, Mueller was able to name 12 of the GRU officers who conducted the breaches: https://www.justice.gov/file/1080281/download. This indictment gets extremely specific, to the point of what software they were running and when, what they were searching for, how they got the funding to buy the VPN access they used to register the Guccifer 2.0 Twitter account, exactly what they said and sent to Wikileaks, etc. This goes into very granular detail. Here's an excerpt:

>Between on or about May 25, 2016 and June 1, 2016, the Conspirators hacked the DNC Microsoft Exchange Server and stole thousands of emails from the work accounts of DNC employees. During that time, YERMAKOV researched PowerShell commands related to accessing and managing the Microsoft Exchange Server.
30.

>On or about May 30, 2016, MALYSHEV accessed the AMS panel in order to upgrade
custom AMS software on the server. That day, the AMS panel received updates from approximately thirteen different X-Agent malware implants on DCCC and DNC computers.

There is essentially a global consensus among intelligence and security organizations, governmental and private, that Russian intelligence was behind the DNC hack and the Guccifer 2.0 persona. By contrast, not a single entity other than the US government backed the Iraq WMD claims, and there wasn't any sort of specific public claims made beyond "they have WMDs". Here, Mueller's reports make hundreds of very specific, narrow claims.

If you like, I could write a 30+ page summary of all of the credible evidence in all of these documents, in addition to hints at what sort of classified evidence US intelligence may have (likely through compromised GRU and Russian government systems, and perhaps also moles, in combination with what the Dutch gave them).

As for whether Assange was aware of any of this or suspected it; who knows. It's very likely "Guccifer 2.0" / GRU would have maintained their cover while sending him information. Doesn't really make sense for them to be like "hey, Russia here, here's some stuff you might want". He's smart, though, and surely was (or at least is now) aware of the possibility.