On a hot morning in August 1892, Andrew and Abby Borden were killed with a hatchet inside their own home in Fall River, Massachusetts. Their daughter Lizzie Borden was arrested, tried and acquitted - and the case was never solved.

In January 1931 a stranger left a message sending an insurance agent to an address that did not exist. When he came home, his wife lay dead in the parlour. He was sentenced to hang, then freed, and the Wallace case has never been solved.

Between 1918 and 1919 someone broke into the homes of Italian grocers in New Orleans at night and attacked the sleeping families with their own axes. The police arrested the wrong people, a letter promised to spare every house playing jazz, and the Axeman of New Orleans was never identified.

In January 1947 a 22-year-old woman was found dead in an empty lot in Los Angeles. The newspapers called her the Black Dahlia. 750 investigators, 500 false confessions and 79 years later, nobody has ever been charged.

In the autumn of 1888, 5 women were murdered in the poorest streets of London. 2,000 people were questioned, 300 were investigated, and the man the newspapers called Jack the Ripper was never caught.

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.