Michael Flynn Win McNamee/Getty Images Special counsel Robert Mueller's investigators are looking into whether former National Security Adviser Michael Flynn took part in efforts to obtain emails deleted from Hillary Clinton's private email server from Russian hackers, The Wall Street Journal reported on Friday.

That 2016 effort was spearheaded by GOP donor and opposition researcher Peter Smith, who told the Journal in May that he lobbied several groups of hackers — two of which that may have included Russian operatives — in search of the roughly 33,000 emails. Smith killed himself days after the interview.

Mueller's investigators, the Journal reported, want to know whether Flynn and his son, Michael Flynn, Jr., were also involved in that effort. It follows Mueller's broad objective to determine whether the Trump campaign colluded with Russians during the 2016 election.

Flynn has remained a central focus of the investigation in the months following his ouster from the Trump administration. Flynn was reportedly one of several Trump advisers that Russian operatives believed could be plied into helping them make inroads with the Trump campaign.

Flynn's time at the White House lasted just 24 days.

He was asked to resign on February 13, with the White House saying he had misled Vice President Mike Pence about conversations he had with Russia's ambassador to the US, Sergey Kislyak, during the transition. But Trump continued to defend him, going as far as suggesting to then-FBI Director James Comey the next day to drop the investigation into Flynn's foreign contacts, according to a memo Comey wrote about the conversation that was cited by The New York Times. Trump fired Comey on May 9.