Mueller in a sentencing memo said Flynn's "substantial assistance" to his probe warrants a light criminal sentence — which could include no jail time for the retired Army lieutenant general.

That assistance, which includes 19 interviews with Mueller's team and Justice Department attorneys, related to a previously unknown "criminal investigation," as well as to Mueller's long-running probe of the Trump campaign's and transition team's links or coordination with the Russian government.

"The defendant provided firsthand information about the content and context of interactions between the transition team and Russian government officials," the memo says.

Mueller's memo almost completely blacks out details of what Flynn might have said.

Robert Mueller doesn't believe Michael Flynn should serve jail time from CNBC.