Prosecutor Brandon Van Grack says "it remains a possibility that General Flynn is continuing to cooperate with the government."

Judge Sullivan had asked Van Grack if Flynn was still cooperating, and Van Grack took several seconds to give that response.

Typically, defendants in this sort of circumstance don't proceed to sentencing until their cooperation is complete, because judges want to be able to fully evaluate how they helped before they are.

"The more you assist the government the more you arguably help yourself at the time of sentencing," Sullivan says.

But Mueller's team and the Justice Department clearly have left the door open for Flynn to continuing to help.

Van Grack is explaining that Flynn by this point has given "substantial assistance."

"The defendant had provided the vast majority of cooperation that could be considered," the former Mueller-team prosecutor tells the judge.

For the first time: The special counsel also acknowledged Flynn’s role in the indictment of two Flynn associates related to their lobbying on behalf of Turkey. Flynn gave "substantial assistance" to the Eastern District of Virginia US Attorney's Office in the Kian indictment unsealed yesterday.

If he had not cooperated and admitted to lying about the Turkish lobbying, Flynn could have been charged in that Virginia federal criminal case, Van Grack said.