On Friday, 26th November 2010, in the close-knit town of Bergamo, Letizia Ruggeri received a telephone call. It was Maura Gambirasio, a mother whose 13-year-old daughter Yara hadn't come home from the gym. Three months later, Yara's body was tragically discovered. With just one piece of DNA evidence to go on, Letizia started a hunt for a perpetrator that would take four years, 20,000 DNA samples, ingenuity and tenacity to find the identity of 'Unknown Male no 1'.