In 1960, the Congo split in two. It was the first of many conflicts that have wracked the nation since. And it was driven by the desire of its native citizens for democracy and equal rights.

Belgium had ruled over the Congo for decades. Its aim was to extract as much wealth as it could from one of the most naturally rich nations on earth. Rubber. Copper. Palm oil. Uranium. Diamonds. Gold. Cobalt.

It landed on a remarkably cruel and efficient method. The Belgians worked the black Congolese population to death, extracting and shipping their own wealth away. Those who objected were made an example of.

By means of exhaustion, sickness, and murder, the regime killed an estimated 8 to 10 million Congolese—about half of the population—between 1895 and 1908. One Belgian historian estimated that the personal profits earned by Belgium’s king at the time, Leopold II, amounted to more than a billion dollars in today’s money.

A form of apartheid continued after that. And then, in January of 1959, a young black Congolese man got into a dispute with a white European driver. It was one injustice too far. He threw a punch that sparked an uprising. Thousands of Congolese clashed with their Belgian colonial rulers over several nights in the capital city, Leopoldville, now Kinshasa.

Their cry for freedom was met with disdain, and a hail of bullets. “We killed them because they were thieves, because they were pillagers,” the Belgian general who led the response said. “If they don’t keep quiet, we are ready to recommence the sport.”

The regime killed an estimated 8 to 10 million Congolese—about half of the population—between 1895 and 1908.

Shortly afterward, his native Congolese soldiers mutinied violently. Many of the Congo’s white European residents, fearful that democracy would come with further retribution, promptly fled to the most mineral-rich province, Katanga. It seceded to form an independent state that was immediately at war with the central government.

It is now something of a forgotten conflict. But it became, briefly, the fevered focus of the U.S., the U.K., and the U.S.S.R., who each backed different players in the Cold War proxy war, and of European white-supremacist mercenaries, who saw defending Katanga as a key first fight in their quest for global domination.

Those mercenaries were funded, in part, by huge mining conglomerates. They wanted to keep Katanga separate so they could continue a lavish flow of profits. If the nation were re-united, the new Congolese central government planned to renegotiate tougher deals to keep hold of its own natural wealth.

It was called the “Congo Crisis.” And at its heart is one of the great unsolved mysteries of the 20th century. On September 17, 1961, a Douglas DC-6 airliner carrying United Nations secretary-general Dag Hammarskjöld and 15 others crashed just beyond the southern border of the Congo, killing all aboard.

Hammarskjöld reviewing troops in the Congo.

Hammarskjöld, a Swedish aristocrat and a deeply principled and idealistic man, had been flying to a negotiation with Katanga that he hoped would end the war, and hand a re-united Congo to its people to decide their own future. His support for independent black rule—free from the influence of either the West or the Soviet Union—meant he was an enemy to nearly all of the interests at play.

His body was found, superficially almost unscathed, with an ace-of-spades playing card placed mysteriously on it. One of his fellow passengers, a security official, briefly survived the crash. Before he succumbed to his injuries and died days later, he reported an explosion on board. Witnesses to the crash on the ground saw another plane in the sky.

Former president Harry S. Truman, a confidant of John F. Kennedy’s, told reporters on September 19 that Hammarskjöld had been deliberately killed. The Congolese prime minister Cyrille Adoula made a similar allegation. They were ignored. And the official inquiry, conducted by the neighboring Federation of Rhodesia and Nyasaland, a government that believed white people should rule over black, declared it an accident.

A small group of people never believed the verdict and kept investigating. Among them were George Ivan Smith, a senior U.N. official and a friend of Hammarskjöld’s, and Claude de Kemoularia, a high-flying French diplomat.

A Meeting in Paris

I often felt that spending five minutes with any of those investigating the death, or those suspected of involvement in it, would have told me much more than any biography.

And soon after I finished my book, I got a chance to listen to two of them. The Bodleian Library declassified, and sent me, a set of archived tapes, recorded in 1981 in Paris, that laid out a startling confession to the murder of Hammarskjöld.

Some record fragments of a conversation between Ivan Smith and de Kemoularia, at de Kemoularia’s apartment overlooking the Bois de Boulogne. Others record Ivan Smith’s own investigations, based on decades of painstaking work.

“On September 17 of this year,” said Ivan Smith on the first tape, “the 20th anniversary of the tragedy, two of his former personal assistants, who had worked very closely with him on a number of major international crises, by arrangement met together in Paris to review the events leading to the tragedy.”

It was called the “Congo Crisis.” And at its heart is one of the great unsolved mysteries of the 20th century.

The story they laid out began on the evening of Thursday, January 12, 1967, at the Palais Garnier opera house, in Paris.

De Kemoularia, by then an adviser to Prince Rainier of Monaco, had been Hammarskjöld’s personal assistant, and was attending an opulent ball there. As he wandered among the hundreds of Parisians in tuxedos and gowns, he bumped into a man he knew. A harried and bespectacled Paris correspondent for United Press International named Robert Ahier.

They spoke of the waves of chaos and change washing over the world. Paris itself would soon be riven by riots. And so the conversation turned, wistfully, to where geopolitics might have been had Hammarskjöld lived.

“Curiously,” Ahier said, “I have come across a man who claims to know, or pretends to know, the truth about the events.”

Two weeks later, by arrangement, a pair of tough-looking men parked an Alfa Romeo outside of de Kemoularia’s expansive quarters in Monaco. One called himself De Troye, and he did most of the talking. The other, Grant, mostly kept watch.

They told de Kemoularia that they had been mercenaries in Katanga. And that a mercenary fighter plane, a Fouga CM.170 Magister jet with 7.5-mm. guns, had shot down Hammarskjöld’s plane.

But they kept repeating that it had been an accident. It had not been the plan. They knew the pilot who had flown the plane. They knew who had killed the secretary-general. But he had been flying a different mission.

De Troye said the pilot’s name was Beukels, and that he had been haunted by the incident. He had dropped in weight from 190 pounds to 110, and was working for a construction company in Belgium between attempts to drink himself to death.

After a few subsequent missed meetings, de Kemoularia became convinced it was a ruse. An attempt to get money out of him. Mercenaries were, well, mercenary about such things. But one Monday night, De Troye arrived with Beukels.

The pilot looked as De Troye had described him: worn thin by life and by the torments of his own mind. He had the ambient acetone smell that comes from years of drinking. But to de Kemoularia, Beukels seemed sincere. Like he wanted to get something off his conscience.

Mr. X

The seceded nation of Katanga, in the cooler south of what had formerly been the Congo, was formally led by a onetime businessman named Moïse Tshombe.

But, the mercenaries told de Kemoularia, it was in fact run by a powerful group of about a dozen European advisers, drawn from Belgium, Britain, France, and elsewhere, and representing industry and other European interests in Africa. It was led by a man they would name only as “Mr. X,” a European executive who was the functional high commander of the Katangese forces and an adviser of such influence that he was more feared than Tshombe.

“I have come across a man who claims to know, or pretends to know, the truth about the events.”

In August of 1961, Hammarskjöld and the U.N. stepped up their peacekeeping operations and attacked Katangese forces in an attempt to end secession once and for all. Mr. X and his cohort feared it was a dangerous sign for the continued presence of Europeans, both in Katanga and across Africa. The U.N. was acting, effectively, as an independent force for the reunion of the Congo—somewhat against the will of both the United States and the Soviet Union, and of European business interests. It could not be allowed to stand, for the precedent it might set.

On September 17, 1961, Hammarskjöld’s plane left Leopoldville to fly to the Katangan border for a cease-fire negotiation with Tshombe. But Tshombe, the mercenaries said, had drifted away from the influence of his advisers. Mr. X could no longer trust him.

Mr. X hatched a plan to scramble two interceptor jets to divert Hammarskjöld to a nearby air base. He and his group wanted to talk to Hammarskjöld and find a solution—one in which their power and influence would not wane so quickly as they would with the end of Katanga and the re-unification of the Congo.

They kept repeating that it had been an accident. It had not been the plan. They knew the pilot who had flown the plane.

Beukels said two pilots and two radio operators in two Fougas took off at about 10:40 p.m. local time, as Hammarskjöld’s plane approached the region. Every fifth bullet in their guns was a phosphorous tracer, which would carve a bright parabola in the black skies. None of the aviators knew who was aboard. Only that they were to approach the aircraft with a message, by radio, and fire warning shots if it did not respond:

Call to DC‐6, this is a landing notification. Please divert to base Kamina. We will escort you. Important Europeans want to meet one of those aboard. If you refuse we have orders to use force. Please confirm your acceptance.

They were to give the plane one minute to respond if it was headed toward the runway, and three minutes if it was flying in another direction. Once the DC-6 submitted, the plan was to fly in formation around it and escort it to the meeting with the Europeans.

The other Fouga saw nothing and departed. But at about two minutes to midnight, Beukels said, he realized that he was right above his target. He dove to 6,500 feet, about 650 feet above the DC-6, and radioed the DC-6 with the message he had been supplied with.

“Wait, I will check,” someone aboard the DC-6 replied. Beukels dropped to the right of the DC-6, again on the advice of his radio operator, and flew parallel with it. They then heard the other plane speaking to the air-traffic-control tower. Beukels, now flying a short distance behind the DC-6, felt that the pilot had hesitated and that perhaps he was preparing to pull a trick and land anyway.

He turned to his left, slightly higher than the DC-6, and dropped behind it. He felt he had no choice but to fire warning shots.

He pulled the trigger and felt the gun expel a bright fusillade. He expected to see it arc harmlessly through the night. But to his horror the larger plane began to weave.

“Do you think I really hit it?” he asked his radio operator. “Yes,” the operator replied. He had seen the plane in flames, on the ground.

Beukels said he was horrified. He landed at a mercenary air base at 1:05 a.m. local time. As soon as he stepped out of the aircraft and saw the faces of his superiors, he said, he knew something terrible had happened. He was brought before a panel of senior officers, and members of the control group, and interrogated. He found out then, for the first time, what he had done. He was held for 10 days. He feared he would be killed, without trial or hope of appeal. But he was freed, to begin a life of drifting. After his meeting with de Kemoularia, Beukels disappeared. He has never been found since.


Though the tapes have only recently been made public, details of Beukels’s account had drifted into public view over the years that followed. They were dismissed. He was clearly after money, the consensus went. And why didn’t he, de Kemoularia, or Ivan Smith report the account to the authorities, who might have been able to verify it?

I found out later that de Kemoularia had approached both the French and Swedish governments with the story. They had shut it down. The Swedish diplomat he had met denied ever seeing him, even when confronted with a business card of his that de Kemoularia had kept from the meeting.

There were other strange disappearances and lapses of memory. Shortly after the U.S. government was asked to seek out new details of the crash, in 1992, the F.B.I. spontaneously destroyed records connected to Hammarskjöld. The tape recorders in the tower were said not to be working, and the detailed tower logs that were supposed to back them up went missing. There were, by my count, at least a dozen spies—working for America, Britain, and West Germany alone—on the ground the night that Hammarskjöld died. The official story is that none of them knew anything. Their reports remain deeply classified.

But, over time, alongside Beukels’s account, other witnesses and key pieces of evidence began to surface. Those strands started to weave themselves into a straight line through the thickets. It is referred to in the thriving cottage industry of Hammarskjöld sleuths as “the golden thread,” and following it as it winds toward a startling conclusion is the subject of my book.

This month, as Black Lives Matter protests spread across the world, a statue of that great tyrant King Leopold II was removed in Antwerp, Belgium. A symbolic punishment for his crimes.

Another kind of closure to the era, in my biased view, could be found in American and British intelligence vaults, where at least two former National Security Agency operatives have suggested that secret recordings could finally confirm the events surrounding Hammarskjöld’s death.

Honesty is not a bad place for justice to begin.

Ravi Somaiya’s The Golden Thread: The Cold War and the Mysterious Death of Dag Hammarskjöld will be published on July 7 by Twelve Books