Special counsel Robert Mueller’s office has questioned Deputy Attorney General Rod Rosenstein as it probes the firing of former FBI Director James Comey, people familiar with the matter told The Associated Press on Tuesday.

It is not clear exactly when the conversation took place, or how long it lasted, but Rosenstein is relevant to Mueller’s investigation because he authored a memorandum in May that the White House initially held up as justification for Comey’s firing.

The fact that Mueller’s team would speak with Rosenstein is not surprising given his direct involvement in Trump administration conversations that preceded the May 9 ouster and the evolving White House explanations of it.

But the questioning is nonetheless an indication of investigators’ continued interest in the circumstances surrounding Comey’s ouster, and whether it constituted an effort to obstruct an investigation into potential coordination between Russia and the Trump campaign. Mueller’s team of investigators is expected to interview current and former White House aides in coming weeks as part of that investigation, according to people familiar with the matter.

The people who discussed the conversation with Rosenstein, first reported by The Wall Street Journal, spoke on condition of anonymity to discuss an ongoing investigation. Mueller’s team of investigators reports to Rosenstein, who oversaw the Justice Department’s Russia investigation following the recusal of Attorney General Jeff Sessions.

Rosenstein told The Associated Press in June that he would recuse from oversight of Mueller’s investigation if necessary and warranted, though he has not done so as of Tuesday and it was not clear when or if he intended to.

“As the Deputy Attorney General has said numerous times, if there comes a time when he needs to recuse, he will,” the Justice Department said in a statement Tuesday night.

Rosenstein appointed Mueller as special counsel one week after Comey’s firing, and one day after it was revealed that Comey had alleged in an internal memo that President Donald Trump had asked him to end an investigation into former national security adviser Michael Flynn.

The White House initially explained Comey’s firing by saying Trump was acting on the recommendation of Rosenstein, who wrote a scathing memo about Comey’s handling of the Hillary Clinton email investigation.

But that narrative was muddled days later when Trump, in a television interview, said he would have fired Comey regardless of the Justice Department’s recommendation. It was revealed earlier this month that Trump and aide Stephen Miller had drafted, but not sent, an earlier memo that sought to justify Comey’s firing. That document is now in Mueller’s possession.

Rosenstein has said he stands by the memo and his assessment that Comey mishandled the Clinton email investigation by publicly announcing the FBI’s findings instead of ceding that authority to the Justice Department. But he has also said he did not intend for his memo to be used as a justification for firing.

In a June interview with the AP, Rosenstein said he understood his involvement in Comey’s firing could lead him to eventually step aside from overseeing Mueller’s work.

“I’ve talked with Director Mueller about this,” Rosenstein said. “He’s going to make the appropriate decisions, and if anything that I did winds up being relevant to his investigation then, as Director Mueller and I discussed, if there’s a need from me to recuse I will.”

(AP)