While van der Zwaan is not a central figure in the investigation, filings in his case illustrated Mueller's continuing interest in Manafort and Gates's actions through President Donald Trump's presidential campaign.
Van der Zwaan was a lawyer in the London office of Skadden, Arps, Slate, Meagher & Flom from 2007 to 2017, when the firm worked with Manafort during a decade when he served as a political consultant in Ukraine.
Manafort, 68, has pleaded not guilty to conspiracy, money laundering, and tax and bank fraud charges related to his lobbying work for a pro-Russian political party in Ukraine and former Ukrainian president Viktor Yanukovych. He has asked a judge to toss out charges, saying prosecutors are pursuing conduct that predate his work for Trump.
Gates, 45, who was deputy campaign manager for Trump and worked with Manafort in Ukraine, pleaded guilty Feb. 23 to conspiracy and lying to the FBI in a cooperation deal with Mueller's probe.
Van der Zwaan admitted lying and withholding documents about information prosecutors said was "pertinent" to their investigation: that Gates had been in direct contact during Trump's presidential run with the Manafort associate, identified in court documents as "Person A," an individual who "has ties to a Russian intelligence service and had such ties in 2016."
Prosecutors said when van der Zwaan was interviewed by the FBI in November, he told investigators Gates had informed him that Person A was a former officer of the Russian military intelligence service known as the GRU.
Prosecutors made the allegation without naming the Manafort associate but described his role with Manafort in detail. The description matches Konstantin Kilimnik, the Russian manager of Manafort's lobbying office in the Ukrainian capital, Kiev.
Kilimnik ran Manafort's office in Kiev during the 10 years he did consulting work there, the Post reported in 2017.
Kilimnik has previously denied intelligence ties, telling the Post in a statement in June that he has "no relation to the Russian or any other intelligence service."
A spokesman for Manafort, who is under a court gag order, has previously declined to comment about the van der Zwaan filings.
Van der Zwaan faced a recommended sentence ranging from zero to six months in prison and asked for no prison time for one count of lying to investigators. He made his false statements to Mueller's investigation on November 3, and Skadden said it terminated him that month.
He also is married to the daughter of billionaire German Khan who owns the Alfa Group, Russia's largest financial and industrial investment group.
Van der Zwaan lawyer William Schwartz said that the defendant should not be punished because of who his family is, and deserved credit for the loss of his career, suffering of his wife, who is expecting the couple's first child in August in a difficult pregnancy, and for turning over recorded conversations and other evidence of his guilt.
"It is unusual conduct to make a false statement, and then immediately provide proof of a false statement," Schwartz said, saying for if it were another defendant those tapes "could have found their way to the bottom of the Thames" River in London.
US District Judge Amy Berman Jackson acknowledged van der Zwaan's character and willingness to turn over evidence of his crimes, but said given his means that allowing the defendant to "pay a fine at the door and walk away would not send a message of deterrence. It would do the opposite," Jackson said.
"It is a message that needs to be sent, particularly because you are an attorney," she said.
Jackson said she did not know if van der Zwaan was motivated to join Manafort and Gates for excitement, the money, or was engaged in a deeper "coverup," but that in lying "he put his own interests ahead of the interests of justice" in an investigation of national and international importance into whether the US democratic process was corrupted.
Manafort has acknowledged staying in frequent contact with Kilimnik during the time he worked for Trump's campaign. He has said he met with Kilimnik in person in May 2016 and again in New York City in August 2016, about two weeks before Manafort resigned as Trump's campaign chairman.
