Special counsel Robert Mueller, who is spearheading the federal Russia probe, has called for a data firm that worked for President Trump’s campaign to provide his team with documents, according to a new report.

Mueller asked Cambridge Analytica in the fall to surrender emails from any of its employees who worked for the Trump campaign, the Wall Street Journal reported Thursday. The request, to which the firm complied, had not been reported previously.

The emails were previously handed over to the House Intelligence Committee, which spoke with Cambridge Analytica CEO Alexander Nix on Thursday via a video conference.

The request from Mueller for the documents came prior to reports that emerged in October, showing Nix had reached out to WikiLeaks founder Julian Assange as part of the 2016 campaign concerning stolen emails related to Hillary Clinton. U.S. intelligence agencies claim the emails were obtained by Russian intelligence and provided to WikiLeaks.

Nix admitted in November that he had asked his speaker’s bureau office to reach out to Assange in “early June 2016.” This was after he had read a news report that WikiLeaks intended to publish Clinton-related emails and requested Assange “share that information with us.”

Assange said he did not comply with the request.

The top Democrat of the House Intelligence Committee, Rep. Adam Schiff, told the Wall Street Journal earlier this year that the committee had a “deep interest” in the connections between the data firm and Wikileaks.

Additionally, Rebekah Mercer, a top Trump donor, contacted Nix two months after the company had reached out to Assange and asked if the company could better organize the emails related to Clinton that were being released by WikiLeaks.

She then asked whether this was possible for Cambridge Analytica or the Government Accountability Institute, a conservative nonprofit dedicated to investigative research.

Nix reportedly responded that he had already contacted Assange in June and asked him to share the emails with the company so they could help disperse them, but said Assange had denied his request, according to the Wall Street Journal.

Cambridge Analytica produced data, polling, and research services to the Trump campaign after Nix had been introduced to the campaign by Steve Bannon, who later became the campaign’s chief executive officer and later a senior White House official.

Mueller’s team is conducting an investigation to determine if the Trump campaign colluded with the Kremlin during the 2016 election.