When the U.S. government put out its latest sanctions list on Dec. 19, the man named at the top did not seem especially important. Described in the document as a former Russian intelligence officer, he was accused of handling money and negotiations on behalf of a powerful Russian oligarch. The document did not mention that the man, Victor Boyarkin, had links to the 2016 campaign of President Donald Trump.

A months-long investigation by TIME, however, found that Boyarkin, a former arms dealer with a high forehead and a very low profile, was a key link between a senior member of the Trump campaign and a powerful ally of Russian President Vladimir Putin.

In his only interview with the media about those connections, Boyarkin told TIME this fall that he was in touch with Trump’s then-campaign chairman, Paul Manafort, in the heat of the presidential race on behalf of the Russian oligarch. “He owed us a lot of money,” Boyarkin says. “And he was offering ways to pay it back.”

The former Russian intelligence officer says he has been approached by the office of Special Counsel Robert Mueller, who is investigating possible collusion between Russia and the Trump campaign. Boyarkin’s response to those investigators? “I told them to go dig a ditch,” he says. Peter Carr, the spokesman for the Special Counsel’s Office, declined to comment. Through his spokesman, Manafort likewise declined to comment on his alleged connections with Boyarkin.

But those connections could be potentially important to the Special Counsel’s inquiry. They would mark some of the clearest evidence of the leverage that powerful Russians had over Trump’s campaign chairman. And they may shed light on why Manafort discussed going right back to work for pro-Russian interests in Eastern Europe after he crashed out of the Trump campaign in August 2016, according to numerous sources in the TIME investigation.

‘Our friend V’

When he joined the campaign in the spring of 2016, Manafort was nearly broke. The veteran political consultant had racked up bills worth millions of dollars in luxury real estate, clothing, cars and antiques. According to allegations contained in court records filed in the U.S. and the Cayman Islands, he was also deeply in debt to Boyarkin’s boss, the Russian billionaire Oleg Deripaska, who was demanding money from Manafort over a failed business deal in Ukraine and other ventures.

Boyarkin says it fell to him to collect the debt from Manafort. “I came down on him hard,” he says. But the American proved elusive. In a petition filed in the Cayman Islands in 2014, lawyers for Deripaska, a metals tycoon with close ties to the Kremlin, complain that Manafort and his then-partner had “simply disappeared” with around $19 million of the Russian’s money.

When he reappeared in the headlines around April 2016, Manafort was serving as an unpaid adviser to the Trump campaign. He wanted his long-time patron in Moscow to know all about it.

In a series of emails sent that spring and summer, Manafort tried to offer “private briefings” about the presidential race to Deripaska, apparently, as one of the emails puts it, to “get whole.” Reports in The Atlantic and the Washington Post revealed those emails in the fall of 2017. Among the questions that remained unanswered was the identity of Manafort’s contact in Moscow, the one referred to in one of the emails as “our friend V.”

Even after TIME learned his full name in April, he proved a difficult man to find. His online presence amounted to digital scraps: one photo of him at a conference in Moscow, a few benign quotes in the Russian media from his years selling arms for state-linked companies, and some vague references in U.S. government archives to someone by that name, “Commander Viktor A. Boyarkin,” serving in the 1990s as an assistant naval attaché at the Russian embassy in Washington, D.C. – a job sometimes used as cover for intelligence agents.

Only in early October was a TIME reporter able to track Boyarkin down. In the company of a senior Russian diplomat and two young assistants from Moscow, he attended a conference in Greece that was organized by one of Putin’s oldest friends, the former KGB agent and state railway boss Vladimir Yakunin. “How did you find me here,” was the question Boyarkin asked, repeatedly, when confronted about his ties to Manafort during a coffee break at that conference.

Once he agreed to discuss their relationship, it was mostly to confirm the basic facts, often with a curt, “Yes, so what.” (He did not respond to numerous requests for comment after his name appeared on the U.S sanctions list on Dec. 19.)

The outlines of Boyarkin’s career suggest a life spent at the intersection of Russian espionage, diplomacy and the arms trade. Having served at the Russian embassies in the U.S. and Mexico in the 1990s, dealing primarily in military affairs, he says he turned his focus to the arms trade in the early 2000s. His specialty was the export of small and medium-sized warships and other naval vessels that were produced in Soviet-era shipyards across Russia.

This business kept him in touch with military buyers from around the world, including in various parts of Africa. By the late-2000s, he had put this expertise in the service of Deripaska, whose global mining and metals empire often involved making deals with despots in the developing world.

But his range was broader than that. As Boyarkin tells it, his acquaintance with Manafort goes back to around 2006, the year Deripaska asked both of them to help redraw the map of Eastern Europe.

The Montenegro connection

Montenegro, a tiny Balkan nation on the Adriatic Sea, was an important testing ground for Manafort’s relationship with Deripaska. The oligarch had invested heavily in that country, buying control of a vast aluminum smelter in 2005 that accounted for roughly half of Montenegro’s exports and a sixth of its entire economy. The following year, he decided to support the Montenegrins’ drive to become an independent country. That meant breaking away from its more powerful neighbor, Serbia – and convincing the world to recognize Montenegro as an independent state.

To get this done, Deripaska offered the help of several of his advisers, including Manafort. “They were a good team,” says a senior official in Montenegro who was involved in that vote. “They helped get the support we needed from our international partners,” both in Russia and the West, says the official, who spoke to TIME on condition of anonymity. After the people of Montenegro voted by a margin slightly above 55% to declare independence from Serbia in May 2006, all the world’s major powers recognized the results.

Manafort has been open about his role in this campaign. “I have always publicly acknowledged that I worked for Mr. Deripaska and his company,” he said in a statement to reporters in the spring of 2017. “For example, one of the projects involved supporting a referendum in Montenegro that allowed that country to choose membership in the EU, a measure that Russia opposed.”

In fact, Moscow never tried to stop Montenegro’s independence, and Deripaska would not likely have supported it so robustly without approval from the Kremlin. (In 2007, he told the Financial Times, “I don’t separate myself from the state. I have no other interests.”)

“There was never any real resistance from Moscow [to the independence vote],” says the senior official in Montenegro, who was involved in lobbying for Russian support in the years before and after that referendum. The Kremlin, he says, was only too happy to have another potential ally in Eastern Europe – one that was heavily dependent on Russian investments. The arrangement suited Montenegro’s leaders just fine. “Better the Russians come here with suitcases of money than with columns of tanks,” says the official.

But their relationship with Deripaska quickly soured in much the same way it began—over money. After years of disputes over unpaid debts, the Russian billionaire sued Montenegro in 2014 for seizing the aluminum plant he controlled. The country then sped up its plans to join the NATO military alliance and integrate with the West.

The Kremlin wasn’t pleased. Foreign Minister Sergei Lavrov said in 2014 it would be “irresponsible” and “even a provocation” for another Balkan state to become a NATO member. According to investigators in Montenegro, Russian agents soon began plotting to unseat the nation’s leaders and install a government more friendly to Moscow. By coincidence, the dispute came to a head in the fall of 2016, at the same time as the U.S. presidential race.

About three weeks before the American elections, the people of Montenegro were due to hold a pivotal vote of their own. Depending on the outcome, the government would either shepherd the country into the NATO alliance the following year, or a new set of leaders would take power, most of whom wanted to change course and develop closer ties with Russia.

According to three sources in this opposition movement, known in Montenegro as the Democratic Front, they were counting on help from an American lobbyist who had worked in their country before – and who happened to be fresh out of a job in Washington. His name was Paul Manafort.

Enter Manafort

Having served for three months as Trump’s campaign chairman in 2016, Manafort was forced to resign in mid-August after his links to Russian interests in Ukraine became public. Still deep in debt, he reportedly went around pitching his services as a consultant in the months that followed to a wide variety of foreign leaders, from the Kurds in Iraq to the incoming president of Ecuador.

The TIME investigation found that Manafort was also in contact with politicians from his old stomping ground of Montenegro. Among them was Nebojsa Medojevic, one of the opposition leaders who were then campaigning to unseat the country’s pro-NATO leaders. His ties to Manafort were first reported to TIME by a former associate of Montenegro’s ruling clique, who said the American consultant had met with Medojevic to discuss a possible consulting deal in the fall of 2016.

At first the tip seemed implausible. Why would one of the world’s most prominent political advisers – still fresh from the chairmanship of the Republican presidential campaign – consider working with a group seen as pro-Russian upstarts in a Balkan nation of 600,000 people?

The senior Montenegrin official suggested an answer. “If Manafort got involved here in 2016, it would only be through the Russians,” he said.

At the time, Russian money was indeed flowing into Montenegrin politics. According to the sanctions list posted Dec. 19, Deripaska and Boyarkin were “involved in providing Russian financial support to a Montenegrin political party ahead of Montenegro’s 2016 elections.”

In more than a dozen interviews that TIME conducted this year, officials and political leaders in Montenegro confirmed that Deripaska and one other Russian oligarch bankrolled the pro-Russian opposition in 2016. Two of them said they heard Manafort’s name come up in strategy meetings for that opposition movement.

When asked about Manafort’s role, Medojevic, one of the leaders of this movement, confirmed that he had met with Manafort to discuss a potential partnership in the fall of 2016. He added that the meeting was a disappointment, and that no deal came out of it. In several follow-up conversations, however, he refused to talk about the meeting, saying that his contacts in the West were legitimate and urging reporters not to publish his initial comments.

For Medojevic and the rest of the opposition, the elections in Montenegro did not go smoothly. The day before the vote, a group of men was arrested and charged with plotting to overthrow the government of Montenegro, assassinate its leader and seize power by force – all with abundant help from Moscow. The Montenegrin authorities later charged two agents of Russia’s military intelligence service with masterminding the alleged coup. Several of the leaders of the opposition in that country, including Medojevic, are currently on trial for charges that stem from the alleged coup attempt.

The following year, Montenegro’s parliament overwhelmingly ratified membership in NATO, as pro-Russian demonstrators protested outside. Russia’s foreign ministry said lawmakers were “trampling all democratic norms and principles.” Now, Montenegro is protected by Article 5 of the alliance, which calls for all members to support any state that comes under attack.

This summer, President Trump took issue with that protection. “Montenegro is a tiny country with very strong people,” he said, after being asked by Fox News in July if the U.S. should come to Montenegro’s defense. “They are very aggressive people, they may get aggressive, and congratulations, you’re in World War III.”

Known unknowns

It remains unclear whether Manafort actually provided any services in Montenegro in 2016. His lawyers deny he did any work for any Montenegrin politicians that year. Nor is it clear whether Manafort owes debts to Deripaska and, if so, how much. A court in Virginia convicted Manafort in August on eight charges of bank and tax fraud related to his lobbying work in Ukraine; he is due to be sentenced in February.

Boyarkin, for his part, denies having anything to do with Montenegrin politics. When TIME met him in Greece, he said he had not worked for Deripaska since the end of 2016. The U.S. government differs on that point; the Dec. 19 press release from the Treasury Department said Boyarkin “reports directly to Deripaska and has led business negotiations on Deripaska’s behalf.”

Those negotiations, involving mining deals in Africa and factories in Europe, were of secondary concern to U.S. investigators when they contacted Boyarkin last year, he says. They wanted to know about his links to Manafort, and the “private briefings” he had offered to Boyarkin and his boss. “They asked about all of that, yes,” the operative recalls. Once again, he says he told them to get lost.

—With reporting by Jovo Martinovic/Podgorica, Montenegro and Tessa Berenson/Washington

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