Though seemingly placid from the outside, special counsel Robert Mueller and his team have reportedly spent recent weeks aggressively digging into communications between Trump associates and WikiLeaks before the release of stolen Democratic emails during the 2016 campaign.

According to a Sunday Washington Post report, Mueller has particularly homed in on Roger Stone, who has bragged about his connections with WikiLeaks founder Julian Assange before.

Both Stone and WikiLeaks officials deny any contact.

The relationship between Trump associates and WikiLeaks is paramount to Mueller’s investigation, per the Post, since the emails published through WikiLeaks appear to have been hacked by Russians to disrupt the campaign and sway the election.