Van Der Zwaan, who is expected to plead guilty on Tuesday afternoon, once said on his LinkedIn page that he was an associate in the London office of the global law firm Skadden, Arps, Slate Meagher & Flom.
Here's why Mueller and his team were questioning Van Der Zwaan. He was speaking with investigators about his work with Skadden Arps in 2012 when the firm did work for the Ukrainian Ministry of Justice to prepare a report on the trial of Yulia Tymoshenko.
Prosecutors working for Mueller charged that the lawyer, Alex Van Der Zwaan, lied to Federal Bureau of Investigation agents about his conversations with former Trump aide Rick Gates, who was indicted previous year on charges related to his work on behalf of pro-Russian factions in Ukraine.More news: Woods misses cut after firing 76; 2 share lead
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Mr Van Der Zwaan was charged on February 16 in federal court in Washington and news of the move emerged on Tuesday.
The indictment said these Russians were in contact with "unwitting" members of the Trump campaign and other Americans but no allegations were levelled against anyone for colluding with the Russians, which President Donald Trump has been keenest to establish.
Circumstantial evidence strongly suggests the unnamed "Person A" in this court filing is Paul Manafort - the longtime business associate of Gates, who has also reportedly agreed to plead guilty in the Mueller probe.
Trump continued to fume about the investigation, blaming former President Barack Obama for failing to take his claims of voter fraud seriously.