Alex van der Zwaan was sentenced to 30 days in jail and a $20,000 fine after pleading guilty to lying about his contacts with former campaign deputy Rick Gates and a former Russian intelligence official.
Van der Zwaan, a Dutch national with Russian roots and son-in-law of a prominent Russian tycoon, was a lawyer in London for Skadden, Arps, Slate, Meagher & Flom in 2012 when he carried out work for the Ukraine government through Gates and Gates' close associate Paul Manafort.
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In 2016, after Manafort became chairman of Trump's election campaign and took Gates as his deputy, van der Zwaan and Gates both had communications with a person they knew as a former official of Russia's GRU intelligence agency, prosecutors said.
According to the FBI, court documents say, that individual -- identified as "Person A" -- "has ties to a Russian intelligence service and had such ties in 2016."
Van der Zwaan lied to investigators on several occasions about his contacts with both Gates and "Person A," prosecutors said.
After his lies were called out, van der Zwaan began cooperating with investigators, including sharing recordings of his conversations with Gates, "Person A" and with a senior Skadden partner.
While the details of those conversations remain secret, court documents suggest they support the idea of more extensive contacts between the Trump campaign and Russia during the election than the White House has admitted.
Van der Zwaan faced up to five years in jail.
He earned a light sentence based on his cooperation with Mueller's probe, which is focused on whether there was collusion between the Trump campaign and Russian interference in the 2016 presidential election.
US intelligence agencies say President Vladimir Putin himself was behind a hacking and disinformation effort to disrupt the election and boost Trump's chances of winning.
In extracting a guilty plea and cooperation pledge, Mueller's team has kept most of the details of what van der Zwaan told them secret. So it remains unclear whether his information supports collusion allegations.
But the case could add to the pressure the investigation is putting on Trump, his family and top aides.
Mueller's team, formally called the Office of the Special Counsel, said in a filing that "van der Zwaan is in an unusual position of having information related to the office's investigation that is not widely known -- including information that he knows first-hand due to his role in the conduct the office is investigating."
