Special counsel Robert Mueller revealed in a court filing that former top Trump campaign aide Rick Gates had contacts with a former agent of Russia's intelligence service as late as October 2016 – weeks before the election that propelled Donald Trump into the White House.
The communications were disclosed in a sentencing memorandum filed Tuesday night against Alex van der Zwaan, a Dutch lawyer who pleaded guilty to lying to the FBI.
Mueller said Gates and van der Zwaan had numerous calls between September and October of 2016 with a "close business colleague" of Gates and Trump's campaign chief, Paul Manafort.
The colleague, identified in the memo only as "Person A," is alleged to have worked with Gates and Manafort "in connection with their Ukraine lobbying work." Person A is a Ukrainian foreign national who lived in Kiev and Moscow until mid-August 2016, the memo said.
The special counsel alleges that Gates told van der Zwaan of Person A's status as a former officer of Russia's military intelligence wing, which is known as GRU.
The special counsel is investigating Russian meddling in the 2016 election, as well as potential collaboration between the Trump campaign and the Kremlin. Trump has repeatedly denied colluding with the Russians. Gates stayed with the Trump campaign after Manafort was fired in summer 2016, and he served on Trump's inaugural committee. He is also a co-founder of the pro-Trump nonprofit advocacy group America First Policies.
The phone calls between Gates, van der Zwaan and Person A allegedly pertained to a 2012 report tarnishing the reputation of Ukrainian opposition candidate Yulia Tymoshenko and boosting the profile of the country's president, Viktor Yanukovych, who was prosecuting her. Manafort and Gates hired a team from van der Zwaan's law firm at the time, Skadden Arps, to make a case for her prosecution.
In the late-2016 conversations, which the memo said also included a lead partner on the matter, the participants discussed the firm's compensation, as well as the risk of being charged with crimes for the report.
The special counsel said that the calls, which van der Zwaan allegedly recorded, "were memorable":
"In van der Zwaan's recorded conversation with Person A, in Russian, Person A suggested that 'there were additional payments,' that '[t]he official contract was only a part of the iceberg,' and that the story may become a blow for 'you and me personally.'"
Van der Zwaan had failed to produce this evidence to the special counsel's office, which said it obtained the recordings through other means.
The lawyer also knowingly withheld and destroyed other salient documents, including an email from Person A on Sept. 12, 2016, in which van der Zwaan was asked to "exchange a few words via WhatsApp or Telegram."
In the memo, the special counsel considered whether any circumstances surrounding van der Zwaan's case should lessen the severity of the charges against him. They determined just the opposite.
"The defendant presents a scarcity of mitigating factors, and several aggravating circumstances," the memo begins.
After retracing various allegations of his duplicitous behaviors during the investigation, the special counsel notes that "van der Zwaan is a person of ample financial means—both personally and through his father-in-law, a prominent Russian oligarch, who has paid substantial sums to the defendant and his wife."
"Van der Zwaan, in short, is a person to whom every advantage in life has been given, and from whom the government and the professional bar rightly expected candor and uprightness," it said.
The memo notes that van der Zwaan did eventually produced the hitherto withheld documents once their existence had been revealed — but maintained that "he does not deserve credit for adhering to the law."
The special counsel's office declined to comment beyond what was written in the court filing. A lawyer for van der Zwaan did not immediately respond to CNBC's request for comment.
Both Gates and van der Zwaan have pleaded guilty to charges levied by the special counsel.
Van der Zwaan pleaded guilty in February to one count of making false statements to the special counsel's office.
Gates and Manafort had been charged with dozens of counts in multiple indictments, including money laundering and lying to investigators. However, Gates pleaded guilty in February to one count of conspiracy against the United States and one count of making a false statement.
Mueller dropped more than 20 charges from a superseding indictment against Gates in February, shortly after Gates pleaded guilty to the two counts.
The New York Times reported Wednesday that a member of Trump's legal team had raised the prospect of the president pardoning Manafort last year, along with former national security advisor Michael Flynn, who pleaded guilty to charges in Mueller's probe.
Manafort has pleaded not guilty; his trial is scheduled to start in July.