Barrack was interviewed as part of the federal investigation of possible collusion between the Trump campaign and Russia in the 2016 election, according to three people familiar with the matter who spoke on condition of anonymity to discuss private conversations.

The specific topics covered in questions from Mueller’s team were not immediately clear.

One of the people who spoke to AP said the questioning focused entirely on two officials from Trump’s campaign who have been indicted by Mueller: Trump’s former campaign chairman, Paul Manafort, and Manafort’s onetime deputy, Rick Gates. Gates agreed to plead guilty to federal conspiracy and false-statement charges in February and began cooperating with investigators.