Court filings show associate of Manafort, Gates allegedly had ties to Russian intelligence

New court filings assert that a business associate of former Trump campaign chairman Paul Manafort and his deputy, Rick Gates, allegedly had ties to Russian intelligence including during the 2016 presidential campaign when the three were in contact.

Perhaps most strikingly - Gates allegedly knew of those ties.

The sentencing memorandum does not say that the alleged connections to someone with ties to Russian intelligence include any links to the Trump campaign.

The allegations are included in a federal court filing on Tuesday night from Special Counsel Robert Mueller related to next week's sentencing of attorney Alex van der Zwaan, a 33-year old Dutch national who was the fourth person to plead guilty in the ongoing Russia investigation. Van der Zwaan had previously worked with Manafort, Gates, and a person the prosecution referred to only as "a Ukrainian business associate of Manafort and Gates (Person A)" on a Ukraine-based political project.

Mueller told a federal judge in Washington, D.C., that "Federal Bureau of Investigation Special Agents assisting the Special Counsel’s Office assesses that Person A has ties to a Russian intelligence service and had such ties in 2016. During his first interview with the Special Counsel’s Office, van der Zwaan admitted that he knew of that connection, stating that Gates told him Person A was a former Russian Intelligence Officer with the GRU."

A source familiar with the conversations tells ABC News “Person A” is Konstantin Kilimnik, a longtime business employee of Manafort’s, who focused mainly on relationships with international power brokers and government liaisons including in both Ukraine and Russia.

Kilimnik did not respond to ABC News’ request for comment.

Van der Zwaan, the son-in-law of a Ukrainian-Russian oligarch, was fired last year from the law firm Skadden, Arps, Slate, Meagher & Flom, according to the firm, after it says it learned of his alleged crime from the special counsel’s team. The firm later agreed to cooperate in the Mueller probe.

Van der Zwaan and his law firm had worked on a controversial 2012 report on the political rival to the then Russia-allied Ukrainian President, himself a longtime client of Manafort, Gates, and "Person A" referenced in the court documents.

Gates - with van der Zwaan - allegedly worked on talking points around the 2012 report and they also continued, allegedly, to work together into 2016, according to the court filing.

Both Manafort and Gates were indicted in October on multiple felony counts including conspiracy, money laundering, and false statements, much of it stemming from their work on behalf of pro-Russian interests in Ukraine.

Manafort pleaded not guilty to all charges, and Gates recently pleaded guilty to reduced charges in exchange for his cooperation in the Mueller probe.

Attorneys for Gates and van der Zwaan did not respond to requests for comment from ABC News, and Manafort and his legal team are under a judge's gag order.

Van der Zwaan's legal team asked the court on Tuesday for no jail time arguing that though he has not been incarcerated since he pleaded guilty in November: “Alex has in many ways been serving a sentence while stuck in limbo…”

“He has been alone, separated from his (pregnant) wife; he has lost his job and his career,” the defense said in its filing noting that he could be at the mercy of immigration authorities should he be thrown in jail. “Alex is desperate to return home to (his wife) as soon as possible.”

The defense also asked that he be allowed to be present for the birth of his child, due in August and to return to help his mother who also wrote to the court pleading to have her son released.

But though the prosecution took no specific position on the request by the defense, the prosecution's motion basically lays out a case for a high fine and/or incarceration, stating that the trained attorney not only "lied repeatedly" in his FBI interview, but he destroyed "pertinent documents" to the investigation.

The court filing also charges that van der Zwaan's billionaire father-in-law, German Khan, has given his daughter and her husband large sums of money, noting of van der Zwaan, "He can pay any fine imposed."

On Tuesday, van der Zwaan is due in a Washington, D.C. federal court for sentencing related to his guilty plea for making false statements. At his plea hearing, the judge discussed a fine and possible reduced punishment of from zero to six months in prison.