Rick Gates, the former aide, told an attorney for a USA law firm that a Russian they worked with in Ukraine was a former military intelligence officer, according to the filing late Tuesday in Washington.
Van der Zwaan is married to the daughter of German Khan, a director and co-owner of Alfa Bank.
"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 GRU".
The case is U.S. v. van der Zwaan, 18-cr-00031, U.S. District Court, District of Columbia (Washington).
As van der Zwaan's February guilty plea revealed, Gates called van der Zwaan in September 2016 and asked him to contact "Person A" - Gates was concerned about possibly facing criminal charges in Ukraine.
In exchange for the guilty plea, Mueller's office agreed not to pursue charges against van der Zwaan in connection with any other false statements he made in November or December 2017, destruction of documents or evidence, or violations of the Foreign Agents Registration Act - which requires individuals who lobby on behalf of foreign entities to register with the USA government - in connection with his work for the Ukrainian Ministry of Justice.
But Van Der Zwaan said he was motivated to lie to hide conversations he recorded with Gates and someone identified only as Person A. Gates had contacted Van Der Zwaan, according to the filing, in 2016 instructing him to contact Person A, who told him the new Ukrainian government might file charges against Van Der Zwaan and other Skadden lawyers with whom he worked on the Tymoshenko report. This individual is also described as being "pertinent to the investigation".
"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, '" prosecutors wrote.
"The relevant questions now - beyond how it may impact the van der Zwaan sentencing - are whether Gates related this connection to anyone else relevant in the Trump orbit, did that person lie to OSC about the issue, did the Trump campaign get anything of value from the Russians, and similar inquiries", he said.
The identity of Person A is unclear.
Mr. Kilimnik has maintained residences in Moscow and Kiev, the capital of Ukraine, and has traveled regularly between them during years of working for Mr. Manafort and Mr. Gates on behalf of various Russia-aligned oligarchs and political parties. In a sentencing memorandum, prosecutors urged the judge to consider a jail term for him.
But the documents say the person is an associate of Manafort's, and the description bears similarities to Konstantin Kilimnik, a Russian-Ukrainian operative who has always been suspected to have ties to Russian intelligence. Last year, as scrutiny mounted of his work with Mr. Manafort and Mr. Gates in Ukraine, he steadfastly denied any association with Russian intelligence.
Oleg Voloshyn, the spokesman for Ukraine's ministry of foreign affairs under Yanukovych, told Bloomberg previous year that he wrote the op-ed article and sent a draft to Kilimnik in early December. Van der Zwaan told the special counsel's office that Gates told him that "Person A" was a former Russian intelligence officer, according to the filing. He added that Kilimnik forwarded it to Manafort, who "advised me to add that the Yanukovych government also worked actively with the United States on nuclear disarmament and with North Atlantic Treaty Organisation".
Last October, The Atlantic also published several emails that appeared to show Manafort using his elevated role in the Trump campaign to work with Kilimnik in resolving a financial dispute with the Russian oligarch Oleg Deripaska. The firm later agreed to cooperate in the Mueller probe. Mueller charged Gates and his business partner Paul Manafort - who managed Donald Trump's presidential campaign between June and August of 2016 - with money laundering and conspiracy over their lobbying work for the government of Ukraine, which ended in 2014.