“This was absolutely not an amateur operation … When you look at the totality of all those pieces and you put them together, it kind of paints a really good picture of who the actor was,” Michael Buratowski, the senior vice president of cybersecurity services at Fidelis Cybersecurity, told ABC News Monday. “I come from a law enforcement background, and it’s [about being] beyond a reasonable doubt. And I would say it’s beyond a reasonable doubt … I’m very confident that the malware that we looked at [was from] Russian actors.”

“When we looked at the malware, we found that it was very, very eloquent in its design as well as its functionality — very advanced, not something that script user or lower level hacker would be able to really generate or customize,” he said…

“We know for a fact that the malicious actors were in there and had access to this data for some time,” he said. “The timing of the release of information from WikiLeaks is very suspect. When you look at it — it was released right before the [Democratic] convention — you have to question what the motivation was behind that.”

Buratowski’s firm was one of three independent cybersecurity firms brought in by another firm, Crowdstrike, to analyze parts of malware that infected computers belonging to the Democratic National Committee. Last month Crowdstrike, which was first to analyze the attack, fingered two Russian hacker groups that the firm said were working for two rival Russian intelligence agencies.