LONDON — America’s National Security Agency may hold crucial evidence about one of the greatest unsolved mysteries of the Cold War — the cause of the 1961 plane crash that killed United Nations Secretary-General Dag Hammarskjold, a commission of prominent jurists says.
Widely considered the UN’s most effective chief, Hammarskjold died as he was attempting to bring peace to the newly independent Congo.
It has long been rumored that his DC-6 plane was shot down, and an independent commission set up to evaluate new evidence surrounding his death on Monday recommended a fresh investigation — citing radio intercepts held by the NSA as the possible key to solving the case.
‘‘The only dependable extant record of the radio traffic, if there is one, will so far as we know be the NSA’s,’’ Commission chairman Stephen Sedley said in his introduction to the report. ‘‘If it exists, it will either confirm or rebut the claim that the DC-6 was fired on or threatened with attack immediately before its descent.’’
Hammerskjold’s aircraft went down on the night of Sept. 17, 1961, smashing into a forest just short of Ndola Airport in modern-day Zambia. A host of hard-to-answer questions about the crash have led to a glut of conspiracy theories.
Among them: Why did it take 15 hours to find the wreckage, just a few miles from the airport? Why did Hammarskjold’s bodyguard, who survived the crash for a few days, say that the plane ‘‘blew up?” Why did witnesses report seeing sparks, flashes, or another plane?
Hammarskjold was flying into a war zone infested with mercenaries and riven by Cold War tension. Congo won its freedom from Belgium in 1960, but foreign multinationals coveted its vast mineral wealth and the country was challenged by a Western-backed insurgency in Katanga, which hosted mining interests belonging to United States, Britain, and Belgium.
They were also jockeying for influence with the Soviet Union, which was trying to spread communism to the newly independent nations of Africa.
All four powers had a stake in the outcome of Congo’s struggle, and all four have been fingered as potential suspects in Hammarskjold’s death.
Three investigations into the tragedy have failed to satisfactorily settle the matter, and the publication of ‘‘Who Killed Hammarskjold?’’ by Susan Williams in 2011 set off a renewed round of speculation — not least because of the book’s reliance on testimony ignored by earlier inquiries.
Zambian eyewitnesses told Williams of a bright flash or a second smaller aircraft pursuing Hammerskjold’s plane.
But one of her most powerful witnesses was thousands of miles away on the night of the crash. In his testimony to the commission, Commander Charles Southall — stationed at an NSA post in Cyprus — said he heard an intercepted radio conversation apparently from the pursuing plane.
‘‘I’ve hit it,’’ Southall said he heard the mystery pilot say. ‘‘There are flames. It’s going down. It’s crashing.’’
The commission’s role was not to weigh in on whether Southall’s — or anyone else’s — testimony was authoritative. But, in a reference to the NSA’s surveillance capabilities, Sedley said it was a ‘‘near certainty’’ that the United States was monitoring radio transmissions from the area.
Sedley said the commission had already sought the help of George Washington University’s National Security Archive, a nongovernmental research center, in identifying whether the NSA had any relevant information.
‘‘Of three documents or records which appear to respond to our request, two are classified top secret on national security grounds,’’ he said. The report went on to cite an expert at the archive as saying it was extremely rare for intelligence intercepts to be made public.
The National Security Archive and the National Security Agency did not immediately return messages seeking comment, and any next steps toward a potential investigation aren’t clear.
The commission — composed of Sedley, Ambassador Hans Corell of Sweden, Justice Richard Goldstone of South Africa, and Judge Wilhelmina Thomassen of the Netherlands — has no official standing, although current UN Secretary-General Ban Ki-moon or individual member states could ask the General Assembly if they want to pursue its findings.
That could lead to an assembly resolution, which might eventually lead to a formal investigation.
In a statement, the United Nations said it would study the report.
‘‘Secretary-General Dag Hammarskjold gave unparalleled service to the United Nations and paid the ultimate price,’’ the statement said. ‘‘The United Nations is among those most concerned in arriving at the whole truth of the circumstances leading to his death.’’
After Hammarskjold’s death, there were three officials inquiries into the circumstances that led to the crash: the Rhodesian Board of Investigation, the Rhodesian Commission of Inquiry, and the United Nations Commission of Investigation. All failed to reach a definitive conclusion.
Hammarskjold, who was a professor of economics at the University of Stockholm, began his career in public service as an economic adviser to the Swedish government.
He was elected secretary-general in 1953 and reelected in 1957. He drew up a set of rules for his staff of 4,000 people, defining their responsibilities to the United Nations and affirming their independence from national interests.