Mueller just subpoenaed the social media adviser for Roger Stone's Trump super PAC

Special counsel Robert Mueller just sent out another pair of subpoenas — this time to a social media expert who worked with Roger Stone, President Donald Trump’s longtime confidant.

Jason Sullivan worked as a social media specialist for Stone’s pro-Trump super PAC, the Committee to Restore America’s Greatness, for several months in 2016. Last week, he received two subpoenas from Mueller as part of the investigation into Russian meddling during the 2016 presidential campaign, Knut Johnson, Sullivan’s lawyer, confirmed to multiple news outlets.

One of the subpoenas summoned Sullivan to appear before Mueller’s grand jury, the other requested documents from him. Sullivan’s subpoenas suggest that Mueller might be focusing part of his efforts on Stone, but when he appeared before the U.S. House of Representatives Intelligence Committee last September, Stone denied knowing anything about Russian collusion in the election.

“I am aware of no evidence whatsoever of collusion by the Russian state or anyone in the Trump campaign,” Stone told reporters at the time, according to Reuters, who was the first to report on Sullivan’s subpoenas. But Stone insists Sullivan did nothing wrong.

“All of [Sullivan's] activities, as far as I know, are perfectly legal,” Stone told ABC News on Wednesday.

On Wednesday, Stone, who advised Trump during the early days of his campaign, told ABC News that Sullivan worked for him “for a couple of months.”

During those months, Stone’s social media activity caused quite a bit of commotion. He focused on Hillary Clinton's campaign chair John Podesta’s hacked emails fervently, and in the weeks before WikiLeaks published Podesta’s emails, Stone alluded to knowing about the drop.

“Trust me, it will soon the Podesta's time in the barrel. #CrookedHillary,” Stone tweeted about six weeks before Podesta’s emails became public. Days before the release, Stone tweeted, “Wednesday @HillaryClinton is done. #Wikileaks.”

Sullivan’s social media techniques involved utilizing software he developed to sift through Twitter and return with a published dataset for clients to use, Sullivan’s lawyer Johnson told ABC News.

In a strategy document Sullivan created for Stone, which was seen by Reuters, Sullivan described this system as creating Twitter “swarms” as “an army of sophisticated, hyper-targeted direct tweet automation systems driven by outcomes-based strategies derived from REAL-TIME actionable insights.”

“Welcome To The Age of Weaponized Social Media,” the document said.

For example, Reuters pointed out that on Election Day, after Trump tweeted, “TODAY WE MAKE AMERICA GREAT AGAIN,” Sullivan used his social media “swarm” on the tweet to boost voter turnout for Trump, by pummelling pro-Clinton social media postings. Trump’s tweet was retweeted more than 325,000 times.

“He's got really powerful technology that he developed and does a fantastic job with it,” Johnson, Sullivan’s lawyer, told ABC News. “I can see why a campaign would want to use him.”