A spokesman for Mueller issued a statement on Friday saying: "A federal grand jury in the District of Columbia has returned a third superseding indictment today against Paul J Manafort Jr, 69, of Alexandria, Virginia, which adds Konstantin Kilimnik, 48, of Moscow, Russia, as a defendant and charges both defendants with conspiracy to obstruct justice and obstruction of justice".
In a court filing Monday night, attorneys with the special counsel accused Manafort of "attempting to tamper with potential witnesses" while awaiting his trial, which thereby "has violated the conditions of his release".
The indictment serves a strategic goal in raising public awareness about the connections that those who worked on Trump's campaign had with Russians, and it serves a legal objective by putting more pressure on Manafort to become a cooperating witness, said Katie Phang, a former prosecutor and partner at the Berger Singerman LLP law firm in Miami.
Lobbying records filed past year by the firm show that it paid $531,000 to Kilimnik in 2013 and 2014, but that covers only a fraction of the time he worked for Manafort.
In the summer of 2016, Manafort emailed Kilimnik and told him to offer private briefings on the USA presidential campaign to Deripaska in an effort to resolve the dispute, people close to the situation have said.
Before Kilimnik was identified by name in charges on Friday, he had made multiple appearances in Mueller's filings as an unidentified intermediary for Manafort.
Along with his former business associate Rick Gates, Manafort was initially indicted in October 2017 on multiple counts that included: conspiracy against the us, conspiracy to launder money, false statements and failure to file reports of foreign bank and financial accounts. Mueller's team is asking a judge to review his house arrest and to consider jailing him.
Mueller's office filed court papers Monday accusing Manafort of witness tampering. Kilimnik was also involved in that episode.
In the court filing earlier this week Mueller accused Manafort of attempting to call, text and send encrypted messages in February to two people from "The Hapsburg Group", a political discussion group he worked with to promote the interests of Ukraine.More news: Pep Guardiola Denies Racism Allegation, Calls It A Lie
The witnesses worked with Manafort in organizing a group of former European officials who lobbied within the USA without registering as required by law.
The government has not charged Manafort with the crime of witness-tampering or obstruction of justice. It isn't clear yet whether Kilimnik might appear in court in Washington.
That is significant because any lobbying or public relations in the United States on behalf of foreign politicians, governments or companies would trigger an obligation under the Foreign Agents Registration Act to disclose those activities to the Department of Justice.
Prosecutors said the two didn't respond to the communications from Manafort and the associate, with one of them telling prosecutors he believed they were trying to induce him to commit perjury.
They said Manafort's "limited communications can not be fairly read, either factually or legally, to reflect an intent to corruptly influence a trial witness".
Friday's indictment was the first time Kilimnik has been named, having only been referred to as "Person A" so far.
Kilimnik has denied to journalists that he has any connection to Russian intelligence.
Asked on Friday if he would pardon Manafort, Trump refused to answer.
Through a spokesman, Manafort has confirmed the authenticity of the emails but said no briefings occurred.