A documentary by Mads Brügger. In English, Danish and French, with English subtitles. Rated PG

Catnip for conspiracy theorists of all stripes, the two-hour-plus Cold Case Hammarskjöld uses one unsolved mystery as a jumping-off point for secret (and not-so-secret) machinations still haunting us today.

That mystery involves the death of Dag Hammarskjöld, the first really hands-on Secretary General of the United Nations.

An aristocratic Swedish economist and diplomat who helped formulate the Marshall Plan to rebuild postwar Europe, he got the top job in 1956, just as the decolonization of Africa and Asia was in full swing.

He was particularly interested in protecting the rights of new African nations, scrambling to keep resources that had been plundered by France, Britain, Belgium, and others for centuries. According to Danish filmmaker Mads Brügger, a Moby-looking trickster who has previously gone after illicit traffic in tobacco and blood diamonds, the UN honcho was killed when his advocacy got in the way of mining interests being fought over in the former Belgian Congo.

Working with Swedish aid worker Göran Björkdahl, investigating this cold case for years, Brügger goes to a number of spots associated with Hammersköld’s violent demise.

He gets close to a Belgian colleague of the mercenary jet pilot who probably shot Dag’s plane down just as it was arriving in Zambia. The diplomat was found, apart from the other charred bodies, with a playing card stuck in his collar. (The Ace of Spades, if you must know.) And the craft was quickly buried after a cursory investigation.

In one of the most laughable episodes, our Scandinavian snoops attempt to locate and dig up the plane, before being stopped by a bemused groundskeeper.

What the movie does excavate, most chillingly, is the connection between those mercenaries and a shadowy group called the South African Institute for Maritime Studies.

Further discoveries, not all confirmed, involve the CIA, AIDS research, and Karen Silkwood–type murders. For more, you just have to see the movie.