Special Counsel Robert Mueller’s office said on Tuesday that President Donald Trump’s former national security adviser Michael Flynn cooperated with its probe into possible collusion between Trump’s election campaign team and Moscow, and it asked a federal judge not to sentence him to prison.

Prosecutors said in a court filing that Flynn had provided “substantial assistance” in Mueller’s probe, including giving “firsthand information about the content and context of interactions between the transition team and Russian government officials.”

They also said he provided help on other criminal investigations, although those details were redacted because the probes are ongoing.

Flynn, who held the White House job for only 24 days, pleaded guilty in December 2017 to lying to the FBI about his contacts with Russia. He will be sentenced in the US District Court for the District of Columbia on Dec. 18.