Kilimnik was a longtime employee of Manafort's political consulting entities and had done work for him in Ukraine. He is also suspected of having connections to Russian intelligence services.
The indictment accuses Manafort, while being confined to his home, of conspiring with Kilimnik to influence two potential witnesses against Manafort between late February and April.
The witnesses are identified as "Persons D1 and D2" in the superseding indictment. That is exactly how Mueller, in his bail revocation request, identified two witnesses who had worked with Manafort and whom he allegedly tried to tamper with.
The "Person A" identified in Monday's filing by the special counsel as Manafort's accomplice in that effort appears to be Kilimnik.
In that filing, Mueller said that in February, after he filed a second superseding indictment against Manafort, both Manafort and Person A "repeatedly contacted Persons D1 and D2 in an effort to secure materially false testimony concerning the activities of the Hapsburg group." That group was a collection of former senior European political leaders who allegedly acted as third-party paid lobbyists for Ukraine.
Court filings say that Person D1 told Mueller's investigators that Manafort reached out to him on Feb. 26 using the WhatsApp encrypted messaging platform to say, "We should talk. I have made clear that they worked in Europe," referring to the Hapsburg group.
Person D1 told investigators he "understood Manafort's outreach to be an effort to 'suborn perjury'" because both he and Manafort knew the Hapsburg group had done work in the U.S.
Mueller's filings also cited a Feb. 28 WhatsApp message by Person A to Person D2, which said, "Basically P wants to give him a quick summary that he says to everybody (which is true) that our friends never lobbied in the US, and the purpose of the program was EU."
Person D2 turned over that message to Mueller's investigators last month.
Lobbying in the U.S. on behalf of Ukraine would have required the Hapsburg group to register with the American government, which it had not done.