The success of investigative genetic genealogy (IGG) in the US hasn’t gone unnoticed in Europe. After US police announced worldwide that the Golden State Killer had been identified with the application of IGG, the Swedish police and judiciary applied the same method to solve a double murder that had remained unsolved for sixteen years. How did this method come about? A young woman unfamiliar with her real name, age, parents, and origins came up with the idea that private genealogical DNA databases that allow customers to trace their distant relatives could also be used to discover her identity. Since then, in the US many cold cases have been solved with the help of these databases and also the identity of many unidentified human remains has been traced. Questions concerning this new method of investigation arise, to which the beginning of an answer is given here. What does the method entail? Is it allowed to use this method in the Netherlands as well?