New details emerge about 48-year-old said to have ties to Russian intelligence, including the use of a private jet owned by an oligarch close to Putin

A Russian man who is said to have ties to Moscow’s intelligence services will be receiving renewed scrutiny from special counsel Robert Mueller’s inquiry into Russian 2016 election interference, according to former federal prosecutors.

Mueller is investigating Konstantin Kilimnik with assistance from three Kilimnik associates, including Donald Trump’s former campaign chairman Paul Manafort, who mentored Kilimnik as a political operative for pro-Kremlin figures in Ukraine.

What's next for the Trump-Russia inquiry now Sessions has been fired? Read more

Kilimnik, an elusive 48-year-old, has already been charged by Mueller with witness tampering. His most recent business partner has been charged with illegally funneling $50,000 from a wealthy Ukrainian into Trump’s inauguration fund.

Kilimnik was also caught up in Manafort’s apparent intentions in 2016 to use his position at Trump’s side to settle multimillion-dollar debts claimed by their ex-client Oleg Deripaska, an oligarch close to Vladimir Putin, the Russian president.

In addition to Manafort, Mueller’s team is also making use of plea agreements with Manafort’s former deputy, Rick Gates, and with the lobbyist Sam Patten, both of whom were Kilimnik business associates and must cooperate with investigators.

Chuck Rosenberg, a former US attorney in Virginia, said: “It’s a safe bet that prosecutors will be asking the cooperators about conversations they had with Kilimnik and others, and would also likely ask about their knowledge of Kilimnik’s dealings with people like Deripaska.”

Nick Akerman, a former assistant special Watergate prosecutor, said: “If there’s anybody who might provide a connection between the campaign and the Russian government it could be Kilimnik. If anybody can explain the ties, if any, between the campaign and the Russian government, it would be Manafort.”

Interviews with Kilimnik associates, congressional sources, Russia and Ukraine experts, and reviews of records have disclosed previously unreported details about Kilimnik’s work with Manafort and Patten, and other ties to Deripaska, the Russian oligarch friendly with Putin:

• Kilimnik used a jet owned by Deripaska for at least one leg of an oddly timed and brief trip to New York to meet Manafort in early August 2016, according to two sources familiar with congressional investigations. Their meeting took place soon after a meeting that Kilimnik has said he had in Moscow with Deripaska.

• During the decade he worked with Manafort in Ukraine as a translator and fixer, Kilimnik and his boss used a Deripaska plane several times for Moscow trips to meet the oligarch and his associates, according to a former colleague. Manafort made at least 18 trips to Moscow between 2005 and 2011, as McClatchy first reported. Kilimnik accompanied Manafort on most of these trips, which were made primarily for meetings with Deripaska and his associates, according to the former colleague.

• Kilimnik’s work with Manafort dates back longer than is widely known. When Kilimnik was fired from his job heading the International Republican Institute’s (IRI) office in Moscow in early 2005, after he was caught secretly working part-time for Manafort, the pair had been working together for almost a year, two former colleagues said.

• In February 2014, as Ukraine’s pro-Kremlin president Viktor Yanukovych was poised to flee to Russia after a violent crackdown on protests, Kilimnik worked with Patten on a new project. The two arranged meetings in Washington with US officials and other influential figures for Serhiy Lyovochkin, then Yanukovych’s recently departed chief of staff, according to a Ukrainian official. Lyovochkin became a leader of Opposition Bloc, a successor to Yanukovych’s party, and was allegedly the source of the $50,000 that Patten helped illegally funnel into Trump’s inaugural coffers.

Kilimnik did not respond to emails from the Guardian requesting comment, including specific queries about whether he used a Deripaska plane. A reporter who tried to approach Kilimnik’s home in Moscow was turned away by security guards. A spokesman for Mueller declined to comment.

Kilimnik, a fluent English speaker and graduate of a Russian military school who is barely 5ft tall, is recalled by former colleagues as sharp-minded and politically conservative. “He talked a lot about the US,” said one. “He was strongly Republican-leaning.”

Over the years, he helped Manafort rake in tens of millions of dollars for political consultancy and lobbying in eastern Europe. Their big-money clients included Ukrainian oligarchs, Yanukovych’s pro-Moscow party and the Russian oligarch Deripaska, an industrial tycoon estimated to be worth $3bn.

If there’s anybody who might provide a connection between the campaign and the Russian government it could be Kilimnik Nick Akerman, Watergate prosecutor

While working for the IRI – a non-profit funded by the US government – Kilimnik began working on political side-projects backed by Deripaska, according to former associates. They said the extra cash allowed Kilimnik to upgrade his lifestyle with a stylish car and trips to London for parties featuring vodka ice sculptures.

But he was careful to leave little trace of his activities. Colleagues said he was known for avoiding email and photographs, and wiped IRI computer systems on his way out. Some now wonder if it was a product of training. The FBI assesses that Kilimnik “has ties to a Russian intelligence service and had such ties in 2016”, Mueller’s team said in a court filing, in March, in which Kilimnik was described only as “Person A”.

The filing also said Gates, who worked closely with Manafort and Kilimnik in Ukraine, privately specified to an associate in 2016 that Kilimnik was “a former Russian intelligence officer with the GRU”, the agency accused of waging “information warfare” against US politics using social media and email hacking.

Senior justice department veterans told the Guardian that Mueller’s allegation against Kilimnik would have required significant evidence and could be a central area of inquiry for the special counsel’s team.

“It means that intelligence analysts have integrated information from a wide range of sources, considered the reliability of and any uncertainties regarding the information, and explored alternatives,” said Mary McCord, who formerly led the DoJ’s national security division, and is now teaching at Georgetown University Law Center. “I would not expect the special counsel to rely on an intelligence assessment in a court filing unless he had confidence in the assessment.”

Rosenberg thought likewise. “Prosecutors have a duty of candor to the court and would only make representations that they know or believe to be true,” he said.

Some former Kilimnik colleagues are unfazed by Mueller’s allegations. Philip Griffin, who helped hire Kilimnik as a translator for IRI and then lured him away to work for Manafort, told the Guardian that Kilimnik’s intelligence ties during his years working with him in Ukraine never worried him.

“It never occurred to me that it would be a big deal if he was reporting to Moscow,” Griffin said. “Is there such a thing as an ex-spy? It didn’t concern me.” Griffin said Kilimnik served as a key strategist for Manafort: “He helped Paul have an insight into the Russian mind.”

A key question for Mueller’s prosecutors is whether Kilimnik played a role, and if so what, in a Russian cyber-operation aimed at sowing discord in the 2016 elections and – according to the conclusions of US intelligence – helping Trump win.

As Mueller’s interest in Kilimnik increased last year, Kilimnik abruptly left Kiev with his wife and two children and moved to Moscow, where he had lived in the late 1990s and early 2000s. He is now living in a gated community in Khimki, the same Moscow suburb that houses the GRU unit accused by Mueller in an 11-count indictment in July of spearheading the hacking of Democratic emails in 2016.

Facebook Twitter Pinterest Donald Trump at the Republican convention in July 2016 with Rick Gates, left, and Paul Manafort. Photograph: Brooks Kraft/Getty Images

Kilimnik is known to have visited the US in May and August 2016 to see Manafort, reportedly to discuss outstanding financial issues with their Ukraine work. Deripaska has alleged in a lawsuit in New York that he is owed $25m by Manafort and Gates after they used his money in a failed cable investment in Ukraine on which Kilimnik worked.

Right after Manafort joined the Trump campaign in March 2016, he and Kilimnik began emailing and brainstorming about avenues to escape the Deripaska litigation threat and improve ties with the powerful oligarch, who according to the AP once was paying them $10m annually.

Soon after Manafort was hired by Trump – initially to help round up enough party delegates to win the Republican nomination – he emailed Kilimnik to make sure Deripaska knew of his key role and suggesting they find a way to make themselves “whole” with him.

In July 2016 emails first disclosed by the Washington Post, Manafort floated a scheme to offer the oligarch “private briefings” on the Trump campaign, and told Kilimnik to pass along the proposal to Deripaska, apparently in an effort to gain favor with the oligarch and settle Deripaska’s lawsuit. Manafort, Kilimnik and Deripaska have all said no such proposal was ever formally made.

Just before meeting Manafort in New York in early August, Kilimnik said in an email to his former boss that he had met with Deripaska for five hours in Moscow and that the oligarch had raised important issues about his “country’s future” that they needed to discuss.

Kilimnik didn’t identify Deripaska in his email to Manafort by name, but coyly referred to the “guy who gave you your biggest black caviar jar several years ago”, according to the email, which the Atlantic first reported.

Seeming to take pains to be discreet, Kilimnik proposed a quick trip to meet with Manafort to brief him on the talks with Deripaska. “We spent about 5 hours talking about his story, and I have several important messages from him to you. He asked me to go and brief you on our conversation.”

Kilimnik added that he told Deripaska he had to “run it by you first”, but is ready to come “provided that he buys me a ticket. It has to do about the future of his country, and is quite interesting.”

And Kilimnik said he could come quickly, “even next week”. Manafort replied that Tuesday 2 August would be best, and the two men reportedly met that day at the Grand Havana Room, a cigar bar in in midtown Manhattan.

Congressional investigators have been interested in the coincidence that a Deripaska owned Gulfstream G550 jet arrived the airport in Newark, New Jersey, very early on 3 August and departed later that day. Two sources familiar with the inquiries said they have “reason to believe” Kilimnik was on the flight back to Moscow.

Deripaska rejects this. Asked whether Kilimnik used a Deripaska jet for his trip, a spokesperson for the Russian oligarch said: “We vigorously deny all these allegations and false information which has no ground and is being plotted by someone who for more then (sic) a year has been unsuccessfully trying to develop a story which does not exist.” It was not clear who was being blamed for the alleged plot.

Previously, a Deripaska spokesperson told Vice News that the plane was only used by the oligarch’s family members to make a quick shopping trip to the US.

Deripaska’s spokesperson also flatly denied earlier that the oligarch “directly or indirectly communicated with Manafort in 2016”, an assertion that is at odds with Mueller’s court filings and Kilimnik’s July emails with Manafort.

Basic Element benefits from a close relationship with the siloviki – the ex-security officials who serve as Kremlin powerbrokers Mike Carpenter

The close proximity of Kilimnik’s New York and Moscow meetings is a logical area for Manafort and Gates to be questioned about by Mueller’s office, said Akerman, the former prosecutor.

Two and a half weeks after Kilimnik’s New York meeting, Manafort abruptly left the campaign on 19 August, after reports of a secret ledger in Ukraine showing $12.7m in off-the-books cash payments that Manafort received over several years from Yanukovych’s party.

In September 2016, Deripaska was visiting New York where he had a surprise visit from FBI agents who tried unsuccessfully to get his cooperation with their initial inquiries into Russia’s meddling in the 2016 election, as the New York Times first reported.

This April, Deripaska and some of his companies were among seven Russian oligarchs, 12 companies they owned or controlled, and 17 Russian government officials who were hit by treasury department sanctions for “malign activity” worldwide “including attempting to subvert western democracies, and malicious cyber activities”.

Deripaska’s company, Basic Element, has its own Russian intelligence ties. An aluminum and energy giant, Basic Element has long employed a former high-level intelligence operative with Russia’s FSB, who this year became the company’s chief executive. The executive, Valery Pechenkin, served in a key security position for more than a decade with Basic Element before his promotion.

Mike Carpenter, a top Russia policy official in the Pentagon during Barack Obama’s administration, said the case exemplified how the public and private sectors had been “captured by the ex-KGB elite” in Russia.

“Pechenkin is a former KGB officer who served as FSB deputy director for counterintelligence when Putin was the agency’s director,” said Carpenter. “Basic Element certainly benefits from having a close, symbiotic relationship with the siloviki – the ex-security officials who currently serve as Kremlin power brokers.”

Mueller’s team is also likely to have grilled Patten for everything he knows about Kilimnik. In August, prosecutors announced Patten had admitted to using a US company that he and Kilimnik formed to illegally funnel $50,000 from Lyovochkin, the wealthy pro-Russian Ukrainian politician, to Trump’s inauguration fund. As part of a plea deal, Patten agreed to cooperate fully with Mueller’s investigation.

Patten, a fellow veteran of the IRI in Moscow, formed the company with Kilimnik in Washington in 2015. Together they did political consultancy work in Ukraine and unregistered lobbying in the US, according to court filings, and were paid more than $1m in all. A spokesperson for Lyovochkin denied he had supplied the funds. Kilimnik was not charged in Patten’s case.

Investigators will also be reviewing emails and other communications sent by Kilimnik since 2016. When charging Kilimnik in June with obstructing justice, Mueller published more than a dozen messages Kilimnik sent to a pair of witnesses early this year over the encrypted messaging applications WhatsApp and Telegram.

“My friend P is looking for ways to connect to you to pass you several messages,” Kilimnik wrote in one message. “Can we arrange that.” Kilimnik and Manafort are charged with conspiring to urge two associates to lie in order to cover up unregistered lobbying work in the US by influential European figures they had recruited in a secret scheme to help Yanukovych bolster his image in America.

FBI asked to investigate suspected double hoax against Mueller Read more

Before that, Mueller’s team caught Kilimnik and Manafort emailing about ghost-writing an article defending Manafort, which was to be published in the name of a former Ukrainian government spokesman while Manafort awaited trial in Virginia this year. The discovery led a judge to reprimand Manafort, who was ultimately convicted on eight counts of bank fraud, tax evasion and other financial misdeeds.

Another Kilimnik link with Manafort was highlighted during the trial, when testimony indicated the Russian was listed as the beneficial owner on some of the 31 offshore accounts that were used by Manafort in his financial scheming.

Perhaps significantly, Mueller court filings also revealed that Kilimnik had numerous contacts with Gates in the weeks just before the 2016 election.

John Herbst, a former US ambassador to Ukraine, who now directs the Atlantic Council’s Eurasia Center, said he thought it “highly likely” that Kilimnik retained his ties to Russian intelligence through the 2016 elections. “It would be in his interest to keep them informed and channel information to them,” said Herbst.