By Paul Callan

Late Tuesday evening, special counsel Robert Mueller revealed a critical scrap of information about the cooperation of President Trump's former national security adviser, Michael Flynn, in Mueller's ongoing investigation. In customary fashion for the often-inscrutable Mueller, the revelation appeared in the form of Mueller's sentencing recommendation for Flynn -- an official court document, rather than a press release or news conference.

US District Judge Emmet Sullivan is scheduled to sentence Flynn on December 18 on charges of lying to federal investigators, a crime that carries a potential maximum sentence of five years in federal prison under federal sentencing guidelines. The special counsel's heavily redacted document suggests that given Flynn's "substantial assistance" to the investigation -- including meeting for 19 interviews -- a sentence "at the low end of the sentencing guidelines" including one "that does not impose a term of incarceration -- is appropriate and warranted." While commenting on Flynn's extensive history of both military and public service to his country, the special counsel also delivered a backhanded slap, noting that given such a distinguished record, the general should have been "particularly aware of the harm caused by providing false information to the government."

Federal judges, though not legally bound by a prosecutor's recommendations, usually follow them. The defense will submit sentencing recommendations to the court later in the week, so slap aside, overall, this is very good news for Michael Flynn.

It's also an important step toward Mueller's endgame with respect to witnesses cooperating with his probe. Mueller's sentencing recommendation is the first of an expected troika of sentencing documents scheduled to be filed this week pertaining to Flynn, Paul Manafort and Michael Cohen.

Sentencing recommendations for former Trump campaign manager Manafort and personal counsel Cohen will likely be filed shortly. Together with the Flynn recommendation, we should view these documents as a legal Rosetta Stone enabling a more accurate translation and understanding of the contents of the final report Mr. Mueller is expected to issue at the conclusion of his investigation.

These sentencing recommendations will be a sound decoder of what's to come because they pertain to the three most prominent Trump advisers netted by the special prosecutor in the 18-month investigation, often referred to by the President as a "Witch Hunt" conducted by a conflicted special counsel heading a team of "Angry Democrat Thugs" prosecutors. (Mr. Mueller, who has been a lifelong Republican and former FBI director under presidents from both parties, was appointed by yet another Republican, Deputy Attorney General Rod Rosenstein -- after Republican Attorney General Jeff Sessions recused himself from any involvement in the probe given his active role in the Trump campaign.)

Flynn, who served as President Trump's national security adviser for less than a month and stands accused of making multiple false statements to Department of Justice entities about his discussions with then-Russian Ambassador to the United States, Sergey Kislyak, has been charged with filing false statements in violation of the Foreign Agents Registration Act in connection with work on behalf of the government of Turkey.

The Flynn controversy also garnered embarrassing headlines for the President when former FBI Director James Comey claimed that the President urged a non-committal Comey to "...see your way to letting this go, to letting Flynn go." Mr. Trump would later fire Comey. The President has denied Comey's claim, though Trump critics have argued that the firing of Comey was a criminal "obstruction of justice" by the new President.

Flynn remains a seminal figure in the Mueller investigation who had largely disappeared from public view since his resignation and subsequent indictment on these federal charges. Mueller's "Rosetta Stone" sentencing documents suggest that while Flynn was out of sight, he was actively providing valuable assistance to the special counsel in other unnamed investigations purposefully redacted from the court document. Most often such redactions occur to allow such investigations to continue in secrecy.

Mueller's warm endorsement of Flynn's cooperation should prove worrisome to the President and his lawyers, particularly in light of the redactions suggesting other secret investigations yet to be completed. The Flynn guilty plea and Mueller's recommendation of leniency suggests further that the investigation has established a clear Russian connection in addition to the widely-discussed Trump Tower meeting and other contacts with lower-level campaign officials. The redacted sentencing document undoubtedly contains other details about the purpose and implications of Flynn's cooperation in these investigations. All of this suggests that Mueller's probe is far from completion.

For the impatient, it would be wise to remember that it took over two decades to decipher the Rosetta Stone after its discovery in 1799. Mr. Mueller, on the other hand, has been investigating the Trump campaign's relationship with the Russians for only 18 months -- but will probably disclose a sizable outline of the scope and direction of his investigation in documents likely to be filed by Friday.