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Lobbyist Sam Patten provided “substantial assistance” to special counsel Robert Mueller and several other ongoing investigations, federal prosecutors said Monday, paving the way for him to potentially avoid jail time at his sentencing this week.

The case has been full of intrigue from the beginning, given Patten’s connections to several prongs of Mueller’s investigation. He founded a company with a suspected Russian operative, steered foreign money to President Donald Trump’s inauguration, was closely tied to Trump campaign chair Paul Manafort, and advised the controversial data firm Cambridge Analytica.

Prosecutors from the US attorney’s office in Washington didn’t recommend a sentence for Patten, who first came under investigation by Mueller’s team. He pleaded guilty in August to illegally lobbying on behalf of a Ukrainian political party that favors closer relations with Russia.

The prosecutors said Patten’s cooperation was “immediate” and “substantial.” They told the judge that Patten deserved leniency and formally requested a reduction in his sentence.

“Patten has met with government investigators, in person or by phone, a total of nine separate times to answer numerous questions and explain various documents,” prosecutors wrote. “In all of these sessions, Patten has been honest and straightforward with government investigators.”

But almost all of the details surrounding Patten’s “substantial” assistance will remain secret for now. Both sides said they would submit additional filings under seal with that information.

The court filings revealed that Patten provided evidence against Manafort and was prepared to testify against Manafort at trial. Prosecutors said Patten’s experience as an overseas political constant made him a “valuable resource for the government in a number of other criminal investigations, providing helpful information about additional individuals and entities.”

For his part, Patten asked for probation instead of prison. His lawyers said he never intended to cover up anything related to Russian meddling in the 2016 campaign. When he pleaded guilty, Patten admitted that he illegally funneled money from a Russia-friendly oligarch to Trump’s inauguration fund, and that he lied about it to a congressional committee.

“His crimes were not motivated by greed or a desire to conceal relevant information from the American public or to aid or cover up any potential interference with the 2016 Presidential election,” they wrote. “To the contrary, Mr. Patten’s decisions in this case stemmed primarily from a desire to accommodate his clients’ requests and to present himself in the best possible light after unexpectedly finding himself a subject of the Russian interference investigation.”

That $50,000 donation was a tiny fraction of the $107 million raised by Trump’s inaugural fund. But federal prosecutors in the Southern District of New York are now investigating that committee for a slew of potential crimes, including fraud, money laundering and conspiracy. It’s not clear if Patten helped with that investigation, which appeared to ramp up earlier this year.

The contribution was not part of a broad effort to inject foreign funds into Trump’s inauguration, his lawyers said. Patten didn’t even like Trump and opposed him in 2016, they added.

“Mr. Patten did not support the Trump campaign and while he may have known people who worked for the campaign at various times, he had no personal connection to it,” his lawyers wrote. “Indeed, Mr. Patten not only openly opposed the Trump candidacy but even broke with his party when he voted for President Trump’s opponent in the 2016 presidential election.”

In his first public comments about his crimes, Patten submitted a letter to the judge expressing remorse and describing how his actions triggered a “very dark” period for him and his family.

“In the eight months since I pleaded guilty before you, and more than a year since this journey began for me, I have changed,” Patten wrote in the two-page letter, which was dated March 28. “To an even more meaningful degree than the day the FBI came to my door, I have surrendered. But in admission and surrender, I have also come to know a certain peace.”

Patten, who said in court last year that he was receiving treatment for anxiety and depression, has given up drinking and attended more than 150 meetings of Alcoholics Anonymous since his guilty plea, his lawyers said. They submitted 45 pages of letters asking for leniency from Patten’s family, friends, his AA sponsor and even his childhood babysitter growing up in Maine.

A sentencing hearing for Patten is scheduled for Friday. Overseeing the case is Judge Amy Berman Jackson, who handled Manafort’s case and several other Mueller prosecutions. Patten’s sentencing was previously delayed while he cooperated with investigators.

This case is unique, as Patten pleaded guilty to a crime that is rarely prosecuted by the Justice Department. Only about 10 people have been charged in the past 50 years with violating the Foreign Agents Registration Act, a federal law that was enacted shortly before World War II.

The small number of comparable cases means Berman Jackson will have “even broader discretion” than usual when she decides Patten’s fate on Friday, prosecutors noted. The maximum potential sentence is five years in prison and a $250,000 fine, though a much less severe outcome seems likely in this case.

Patten’s foreign client was the Opposition Bloc, a Ukrainian political party that favors close ties with Russia. The party was formed by allies of Ukrainian President Viktor Yanukovych after he fled the country amid unrest in 2014. Patten and Manafort worked for some of the same clients, and Manafort was sentenced to 7.5 years in prison for crimes relating to his own lobbying.

CNN’s Kara Scannell contributed to this report.