Special counsel Robert Mueller and his team interviewed Deputy Attorney General Rod Rosenstein over the summer as part of their investigation into Russian interference in the 2016 elections and any potential ties to the Trump campaign.
That would have put Rosenstein in the position of being interviewed by the very special counsel he created, and suggests that Mueller and his team are probing elements of President Trump's firing of FBI Director James Comey.
Rosenstein authored the memo that the president and the White House used as their main justification in firing Comey in May. While Rosenstein has stood by the arguments made in the memo, he also has said it wasn't his intent for the memo to be used for that explicit purpose only.
In May, media reports emerged that suggested Rosenstein was threatening to quit over how the Comey firing was handled and how his role was portrayed, but the deputy attorney general denied the reports.
Rosenstein appointed Mueller as special counsel in May. Attorney General Jeff Sessions recused himself from the Russia investigation in March.
A report by Fox News said sources familiar with the investigation confirmed Rosenstein's interview with Muller's team.
Details of the Comey firing sparked speculation that the president may have obstructed justice because Trump fired Comey not long after he reportedly asked him to "let go" the investigation into Mike Flynn, who served less than four weeks as Trump's national security adviser early in the administration. Flynn had to step down after a transcript of a phone call he had with then-Russian Ambassador Sergei Kislyak was leaked to the media showed the two did discuss sanctions, contradicting earlier statements by Flynn to the vice president and others.