WASHINGTON (Reuters) – U.S. Special Counsel Robert Mueller’s office will make a sentencing recommendation for former national security adviser Michael Flynn on Tuesday, in a court filing that is expected to shed light on the extent of Flynn’s cooperation in the Russia probe.

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 U.S. District Court for the District of Columbia on Dec. 18.

He is so far the only member of President Donald Trump’s administration to plead guilty to a crime uncovered during Mueller’s wide-ranging investigation into Russian attempts to influence the 2016 U.S. election and potential collusion by Trump aides.

Others who have also since been charged by Mueller include Trump’s former campaign manager Paul Manafort and campaign deputy Rick Gates, as well as Trump’s former personal lawyer Michael Cohen who last week pleaded guilty to lying to Congress about a proposed Trump Organization skyscraper in Moscow.

Trump has called Mueller’s probe a witch hunt and has denied colluding with Russia. Moscow denies trying to interfere in the elections.

Flynn’s crime of lying to the FBI carries a statutory maximum sentence of five years in prison. However his plea agreement states he is eligible for a sentence of zero to six months and can ask the court not to impose a fine.

Flynn, a retired army general, was forced to resign after he was found to have misled Vice President Mike Pence about discussions he had with Russia’s then-ambassador Sergei Kislyak.

Under a plea bargain deal, Flynn admitted in a Washington court that he lied when asked by FBI investigators about conversations with Kislyak just weeks before Trump took office.

Prosecutors said the two men discussed U.S. sanctions against Russia and that Flynn also asked Kislyak to help delay a U.N. vote seen as damaging to Israel.

Mueller’s office has had varied degrees of success with the level of cooperation it has received from defendants who have pleaded guilty.

Recently, prosecutors asked for another delay in sentencing Gates, citing his ongoing cooperation in multiple probes.

But Manafort could be facing a tough sentence after prosecutors last month alleged he had breached his plea deal by lying repeatedly to the FBI.

They are due to file court papers on Friday laying out their case for why Manafort should lose any credit when he is sentenced for his alleged failure to accept responsibility for his crimes.