At five in the morning, the sun is already bathing the camper van where Silvia, Javi, and Astrid are sleeping. In front of them, misty forests and coffee plantations in El Salvador shake off the night, and seven-year-old Astrid has already opened her eyes. She knows that today she will visit a volcano. She gets up alone—as she does almost every day since she began an itinerant life—and, without rushing, gets dressed, makes her bed, and washes her face. She looks for binoculars, prepares her water bottle, and adjusts the straps on her backpack. Then she goes out to check if the other family they will be climbing the trail with is ready.

Criminals leave fingerprints, but also traces of what they feel, how they attack, and who they choose. This idea inspired, in the 1970s, a new method at the FBI to understand how the most feared criminals in US prisons thought, as recalled in the acclaimed Netflix series. MindhunterSince then, police investigations have never been the same. Behavior analysis deduces how an unknown offender will act based on the behavior they exhibit during a crime, and since its inception, this discipline has gained ground among elite teams and the most prestigious police forces around the world. Its essence: putting a magnifying glass on the motivations of attackers. "Historically, the police have been primarily concerned with the what, the how, the when, the who, and the where; but we left out the why," says Xavier Álvarez, the first behavioral analyst for the Mossos d'Esquadra (Catalan police). A question that often connects the victim with the perpetrator.

Anna Gual's son was four years old when he had to be operated on for carnots and tonsils at the Hospital Universitari de Terrassa. It was November 3, 2023. Gual entered the operating room lobby with the little boy in her arms. There, they both witnessed the sedation – intranasally – of a crying girl and then she was taken inside. One, two, three, four, five minutes. It was her turn. Pre-anesthesia medication is administered with the aim of reducing the anxiety of patients in pediatric operations. Unfortunately, and unlike that girl, the sedation did not have the desired effect on Gual's son: "He was so nervous that he kept crying." Two nurses then took him away: "They had to tear me from my arms to take him to the operating room; it was traumatic," she laments.