Attorney General Jeff Sessions was interviewed last week by special counsel Robert Mueller as part of the investigation into Russian interference in the 2016 election.

Sessions is the first member of President Trump’s cabinet known to have been questioned by the special counsel’s office in its investigation into possible coordination between the Trump campaign and Moscow.

Justice Department spokesman Ian Prior confirmed Sessions’ interview to NPR on Tuesday. Sessions cooperated voluntarily.

The special counsel’s office declined to comment.

In the interview, which was first reported by The New York Times, Sessions answered questions about the Trump campaign’s contacts with Russians and their proxies during the 2016 presidential campaign.

He’s also understood to have discussed possible obstruction of justice in the firing of FBI director James Comey—a move that Sessions supported.

A former Alabama senator, Sessions became an early endorser of Trump when the real estate tycoon was struggling for support from lawmakers and his chances of winning the White House seemed remote.

Sessions served as a top aide to the campaign, and he helped lead the foreign policy team. Sessions was rewarded for his loyalty with the position of attorney general after Trump’s surprise election win.

But Sessions recused himself from the Russia investigation in March because of his role in the campaign—a decision that has earned him a steady stream of criticism from the president.