The bureau was prepared to close the investigation into Flynn until “the Logan Act stuff,” the official said, referring to phone calls in late December where Flynn reportedly discussed US sanctions with Russian ambassador Sergey Kislyak.

The source brought up the Flynn investigation after BuzzFeed News asked if clear evidence existed tying Trump to Moscow. The official then mentioned the FBI investigation into Flynn. It was not clear if the FBI’s probe was a counterintelligence investigation.

Flynn’s phone calls with Kislyak, first reported by The Washington Post, were a potential violation of the Logan Act, which forbids private citizens from negotiating with foreign governments. At the time of the calls with Kislyak, the Trump team had not yet taken over the US government, and Flynn had yet to take up his new public official role. The Logan Act has never been used to prosecute anyone.

That an investigation was already up and running in December indicates there was concern among the intelligence community about Flynn’s loyalties before his phone calls with Kislyak. After the nature of those calls was revealed by the Post in January, Flynn quickly left the White House for misrepresenting the nature of the calls to Vice President Mike Pence.