According to NBC News, investigators reportedly plan to interview multiple witnesses who may be able to shed some light on Flynn's earlier lobbying work, whether he was ever involved in money laundering, and whether he ever lied to or misled federal investigators regarding his overseas contacts.
Flynn's firm was tasked with fomenting dissent inside Turkey, and with lobbying the U.S. government to extradite Fethullah Gulen, a Turkish cleric living in Pennsylvania, who Erdogan believes is responsible for planning last year's attempted coup. Flynn's son, Michael G. Flynn, worked briefly on Trump's transition team and for his father's lobbying firm, Flynn Intel Group.
Three sources are telling NBC News that Mueller is "applying renewed pressure on Flynn" following the indictment of Paul Manafort.
On Oct. 27, White House Press Secretary Sarah Huckabee Sanders claimed the Trump administration viewed the Russian probe as "getting closer to conclusion" in an interview on Fox News' America's Newsroom.
It was reported that Mr Flynn could face less severe charges if he cooperates with Mr Mueller's team and that could also benefit his son.
White House officials have previously stressed that those charged to date were campaign officials who were not brought into government by Mr Trump.
Additionally, investigators have been digging into allegations that Flynn may have been involved in efforts to facilitate the extradition of Muslim cleric Fethullah Gulen, a vocal opponent of Turkish President Recep Erdogan, from the United States back to Turkey.
According to an exclusive report from NBC News, federal investigators have gathered enough evidence to bring charges against Flynn and his son. It was also unveiled that George Papadopoulos, a former Trump foreign policy adviser, pleaded guilty over the summer to lying to federal prosecutors. The elder Flynn was sacked in February after a disclosure that he had lied to Vice President Mike Pence about Flynn's contacts with Sergey Kislyak, Russia's ambassador to the U.S.
It seems that the objective of bringing or threatening to bring charges against Flynn's son is to intimidate Flynn into protecting his son.