Rose Burkert and Roger Atkison (9 of Diamonds, Iowa)

In September 1980, a Holiday Inn hotel in rural Iowa became the scene of a shocking double murder: a couple was found dead in their hotel bed, covered in lacerations. And the scene around them is one of the strangest and most puzzling I’ve ever come across in all my work. It’s one of the reasons this case has gained notoriety over time: I mean, to this day, the hotel where the couple lost their lives is still visited by true crime fanatics.

Despite multiple suspects – and three agencies contributing to the investigation – no one has ever bee...