Who Killed Hammarskjöld? The UN, the Cold War and White Supremacy in Africa

To paraphrase the singing Reverend Mother in The Sound of Music: "How do you solve a problem like the Congo?" So many have tried and failed and are still trying. In 1961, in the age of African decolonisation, Dag Hammarskjold, the saintly United Nations secretary general, also tried and lost his life in the process. Susan Williams' fascinating book explores the unresolved issues surrounding his death in a plane crash in central Africa. With the help of her engaging and no-nonsense style - part Miss Marple, part No. 1 Ladies' Detective Agency - we are led through the messy, ugly and secretive dark arts of decolonisation in a world of white supremacists and Cold War lunatics. Kids: don't try this at home.

So what was an aristocratic, sensitive and spiritual Swede doing flying around central Africa in the dark? Hammarskjold became UN secretary general in 1953. He quickly established a reputation for high principles, tough negotiation and an uncompromising support for African decolonisation. All these were sorely tested in central Africa by 1961. The Belgians had been kicked out; white Rhodesians were trying to hold on; and the first black African leader of the Congo, Patrice Lumumba, had just been put through the equivalent of a human paper shredder and then pickled in acid. Hammarskjold was desperately trying to bring peace to the province of Katanga, which wanted to secede. The Soviets were against this; the West was for it. The night he was killed he was on his way to meet with Katanga leader Moise Tshombe in a bid to peacefully halt the secession.

Williams begins with a description of Dag (the book doesn't shed any light on the other great mystery surrounding him, namely how you pronounce his surname): "he is wearing a white shirt with elegant cuff-links; his drill trousers are pale, with a slim black belt...he looks almost immaculate and extremely dignified". Bizarrely, this is from a photograph taken after the fatal crash and intense fire, part of new evidence released to Williams by Rhodes House Library, Oxford. Protruding from his tie is what looks like a playing card, rumoured to have been the Ace of Spades - "the death card".

She then introduces the verdicts of three professionals she interviewed: a consultant pathologist, a firearms expert and a forensic photographer. Collectively they suggest that the immediate inquiry conducted by the Northern Rhodesians was at best sloppy, at worst a cover-up. Why was the body not charred? What happened to the initial report of a bullet hole in his head? Were the photos and the subsequent medical reports doctored? And why was the account of the only survivor (who later died of his injuries) not pursued? He said he had heard an explosion before the crash...

In a thesis that encompasses more mysteries than Said Gadaffi's PhD, one of the most intriguing chapters offers the evidence of a US intelligence officer who was then stationed in Nicosia. Listening to high-frequency radio traffic while intercepting messages from Africa, Charles Southall heard the sound of an aircraft engine and the commentary of a pilot describing his apparent attack on the UN-chartered cargo plane: "I've hit it. There are flames. It's going down."

Happily for the publishers, Williams' four years of painstaking research didn't unearth any evidence that the pilot of the UN plane had twiddled the wrong knob before landing or that some other human error had occurred, as the Northern Rhodesian authorities claimed. There is no new definitive proof that Hammarskjold's plane was shot down by mercenaries or white racists, nor that he was shot in the head. But there are enough cover-ups and anomalies in the official inquiries to point to malice at work, and at the very least, a wilful neglect of correct procedural care in his flight and in the subsequent investigation.

Conspiracy theorists and Cold War buffs will always keep his death alive, so to speak. There may be another official inquiry. But thankfully this book, full of historical detail on the region's tragic transition to "freedom", will also bring the legacy of Hammarskjold, the great diplomat, to a new generation of students. Cooperating closely with relatives, as Williams did, runs the risk of producing hagiography, but Hammarskjold's bravery in not being intimidated by the political establishment is indisputable. He doggedly championed African self-determination when outside forces were scrambling for its wealth at the expense of its people. At least he did not live to see so many African leaders do the same.