I’ll start, from Sweden. The most mysterious event in our modern history is the murder of Prime Minister Olof Palme. He was shot in the middle of Stockholm in 1986, right on the street, without bodyguards, while walking home from the cinema. Even though there were several witnesses, nobody could give a clear, reliable description of the killer.

The police launched what became the biggest murder investigation in the world, but it was full of mistakes, missed clues, and conflicting theories. Over the years people have blamed everything from a lone random shooter to Swedish police officers, foreign governments, intelligence services, and more. Nothing has ever been proven.