ST. PETERSBURG -- Special counsel Robert Mueller announced charged 13 Russian nationals and three Russian countries with crimes related to a campaign to sow disinformation and division in the U.S. in the run-up to the 2016 election. According to the indictment, interference effort traced back to a so-called "troll factory" in St. Petersburg set up to influence U.S. voters.

Russia's Foreign Minister Sergei Lavrov denied that the Kremlin was involved, questioning what evidence there is tying the government to the effort. Russian internet activist Lyudmila Savchuk saw the operation with her own eyes. In 2015, she went undercover and got a job at the troll factory writing fake news in Russian. A shaky video is the only glimpse she has now of the group's work.

"I knew there were people working in English. They were better paid than we were and their work was absolutely secret," Savchuk said.

A views of the four-story building known as the "troll factory" in St. Petersburg, Russia, Saturday, Feb. 17, 2018. Naira Davlashyan / AP

That work consisted of posts ridiculing Hillary Clinton and fanning the flames of flames of divisive issues in the U.S. When Savchuk saw those English posts, she recognized them right away as the work of the trolls.

"They used the same techniques we did," Savchuk said.

Yevgeny Prigozhin was the troll factory's boss, according to the indictment. Known as "Putin's Chef," Prigozhin originally made his money in high-end restaurants. He once served President George W. Bush at a state dinner back in 2002.

The U.S. indictment doesn't make a direct link between the troll factory and the Kremlin, but Prigozhin has made millions from Russian government contracts.

"There is no doubt that this factory existed and worked for the Kremlin," Savchuk said.

In Russia, it's dangerous to take on that kind of power.

As if she was afraid, Savchuk said, "To stay safe, I can't answer that question."

The latest evidence says the troll factory's American operations have scaled back, at least for now. But U.S. intelligence agencies are warning there may be a fresh assault in the runup to this fall's midterm elections.