He had sent his bodyguards home. He and his wife walked out of a Stockholm cinema just after eleven at night and turned down a street full of people. What followed became the largest criminal investigation in Swedish history, and it ended in 2020 with a name and no trial.

On a January morning in 1974, three teenagers came home from school and found their parents and their two youngest siblings dead in the house. For three decades the man who did it walked around their city as a church council president. He was caught because he could not stop writing to the police.

For four decades he was three different monsters with three different names, and the men hunting him could not agree that he was one person. The break, when it came, did not come from a witness or a confession. It came from strangers who had spat into a tube to find out where their grandparents were born.