(CNN) Deputy Attorney General Rod Rosenstein continues to oversee special counsel Robert Mueller's investigation after consulting with a career ethics adviser at the Justice Department about his ability to oversee the Russia probe, a source familiar with the matter tells CNN.

For nearly a year, legal experts and journalists have questioned why Rosenstein has not stepped aside from overseeing Mueller's investigation given that he was part of the dramatic firing of FBI Director James Comey. That fact has more recently served as ammunition to attack Rosenstein's credibility by allies of President Donald Trump.

But CNN has now learned that Rosenstein has consulted with the ethics adviser over the course of the investigation on whether he needs to recuse himself, and he has followed that individual's advice -- a fact which has not been previously reported and offers a more fulsome explanation for how he has continued to oversee Mueller's work. The source did not specify the number of conversations, timing, or the details of the advice.

To date, Rosenstein has offered little by way of explanation publicly, but he made clear last year that if he were to become a subject of Mueller's investigation, he would recuse himself.

"I've talked with Director Mueller about this," Rosenstein told the Associated Press . "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."

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