In court documents, including an affidavit by Federal Bureau of Investigation agent Brock Domin, prosecutors with special counsel Robert Mueller allege Manafort and his associate tried to contact the two witnesses by phone and through an encrypted messaging program.
Berman Jackson said information was being withheld because in those instances because "the names of confidential sources who had provided information to the government" were involved and because they contained "information relating to ongoing investigations that does not bear upon the allegations in either of the two cases now pending against Manafort".
Mueller's team asked the DC judge to lock Manafort up, given that he had violated the terms of his bail by interfering with witnesses, writing that there's "little confidence that restrictions short of Manafort's detention assure Manafort's compliance".
Also that week, on February 23, Manafort's longtime deputy Rick Gates agreed to plead guilty to charges of conspiracy and lying to investigators and would cooperate with prosecutors, making Manafort's case an even more hard one to overcome.
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That could result in Mr Manafort, who has been under house arrest since October, being jailed ahead of his trial. Then he wrote: "We should talk".
Manafort reportedly called one of the witnesses to give him a "heads up" about the Hapsburg group, but the witness wisely chose to hang up. Around that same time, Manafort's co-defendant and longtime business associate, Rick Gates, pleaded guilty and agreed to cooperate with prosecutors. The person believed from his experience that the Hapsburg group lobbied in the United States and knew that Manafort knew that as well, the agent wrote.
"Manafort and Person A - who is a longtime associate of Manafort's - repeatedly contacted Persons D1 and D2 in an effort to secure materially false testimony", according to a motion filed in the U.S. District Court for the District of Columbia.
Court papers also accuse Person A of making several attempts to influence the witnesses' testimony in February and later in April.
The FBI said that it had obtained statements from both of the witnesses as well as telephone records and documents Manafort stored on a cloud service, which show his communications with the witnesses.