Just after midnight on September 18 1961, a plane carrying Dag Hammarskjold, the dapper secretary-general of the United Nations, crashed near Ndola in British-run Northern Rhodesia. The Swede was found the next afternoon, unburned but dead beside the charred aircraft. A Rhodesian inquiry blamed pilot error. But that was almost certainly wrong. Most likely, Hammarskjold was murdered. For once, the conspiracy theories are true. That's the conclusion of a startling, meticulous, convincing book, written in the understated prose of a Scandinavian crime thriller, by Susan Williams, senior research fellow at the Institute of Commonwealth Studies in London.

“It's a very well-researched book,” the South African judge Richard Goldstone told me. “A number of people read it and thought something should be done.” An international commission of lawyers including Goldstone is now deciding whether to recommend a new UN inquiry into Hammarskjold's death. That inquiry will surely come. It may even reveal who killed Hammarskjold.

In 1961, the world was watching Congo.