A strong advocate of decolonization, Mr. Hammarskjold certainly had adversaries who felt threatened by his diplomacy. He died while on a visit to help end a secessionist war in newly independent Congo, a former Belgian colony rich with strategically vital minerals, including uranium, coveted by the world’s big powers.
It was a mission regarded with suspicion by powerful mining interests in Belgium and South Africa, as well as permanent members of the Security Council, including the United States and Britain. Mr. Hammarskjold’s work later earned him a posthumous Nobel Peace Prize.
The narrative of his final hours has been one of enduring fascination, laced with cryptic references to shadowy mercenaries, big-power machinations, airplanes parked on darkened runways and distant monitors tracking radio communications as the DC-6 made its fatal, final approach.
The crash came at a pivot in Africa’s fortunes between colonialism and independence, heralding an era when the Cold War split the continent, fueling guerrilla wars and uprisings — from Mozambique and Zimbabwe to Angola and Namibia — that reached their conclusions more than three decades later with the end of apartheid in South Africa.
Frustrated that a definitive answer to what exactly happened to Mr. Hammarskjold’s plane had never been established, his two most recent successors in the top role at the United Nations — Ban Ki-moon and António Guterres — have revitalized the inquiry.
A panel appointed by Mr. Ban found in 2015 that enough new tidbits of information had surfaced to warrant a new investigation. A General Assembly resolution last December authorized the appointment of an “eminent person” to review the information to determine the scope of any new…