Mueller kept grilling witnesses about Michael Cohen -- even after the FBI raided his office: report
Longtime Trump attorney Michael Cohen (Photo Shutterstock).

Special counsel Robert Mueller's team reportedly kept grilling witnesses about what estranged Trump "fixer" Michael Cohen did during the 2016 campaign, even after the FBI raided his office this past April.

Sources tell CNBC that prosecutors in the Russia probe continued asking questions about Cohen's role in Trump's campaign -- as well as questions "about whether Cohen conducted personal business while working as an employee of the Trump Organization and for insight on why he didn't get a job in the Trump White House" -- until at least this past May.

Legal experts who spoke with CNBC said that "Mueller's continued interest in Cohen suggests that he could still be a pivotal source of information to the larger probe into whether Russian operatives colluded with Trump campaign officials to interfere in the 2016 presidential election."

The questions about Cohen came despite the fact that Mueller's team had already passed on incriminating information it had found on the former Trump attorney to the U.S. Attorney for the Southern District of New York, which proceeded to seek authorization for a raid on Cohen's office.

Cohen last week pleaded guilty to eight separate charges, including for tax fraud and for making an illegal campaign contribution to Trump's campaign in the form of "hush money" payments made to former Playboy model Karen McDougal and adult film star Stormy Daniels in exchange for their silence about past affairs.