On 2 January 2012, 18-year-old Myles Williams broke into the family home of his girlfriend, Kirsty Treloar, and murdered her in front of their 26-day-old baby. He also stabbed Kirsty's sister Gemma twice and brother and brother Dean three times in the chest before dumping Kirsty’s body in an alleyway. The previous night, Williams had sent Kirsty a text with a new year's resolution promising not to hit her again. Twelve hours later, he killed her. For the first time on television, in this incredibly emotional and powerful programme, we hear from all of Kirsty's family who were there that night. With expert analysis from forensic psychologist Dr Keri Nixon and psychologist Emma Kenny, we profile Williams and reveal the horrific impact his actions had on a loving family.