Beginning in 1989, this episode tells the story of a murder in Billingham, Teeside, that would lead to one mother challenging an 800 year-old law. In November 1989, a young single mother called Julie Hogg disappeared without word, leaving her parents and young son distraught. Three months later her body was found and a suspect arrested. Weaving together interviews with Julie’s mother Ann Ming and Julie’s son Kevin, as well as friends, journalists, police officers and leading politicians, the programme tells the story of how Ann's actions came to overturn the law on Double Jeopardy. After a jury failed to convict her daughter’s former boyfriend Billy Dunlop, Ann fearlessly took on the political and legal establishments, knowing that unless the law was reformed, he would never face a re-trial. After years of tireless campaigning, Ann finally succeeded and in 2006 Dunlop was tried again - and became the first person to be convicted under the newly reformed double jeopardy law. As this episode traces the twists and turns of Ann’s campaign, the story of other cases that benefitted from the legal changes are also explored, from Gary Dobson and Clifford Norris - the killers of Stephen Lawrence who were convicted in 2012 - to the killer of Surjit Chokkar, who was finally convicted 18 years after his murder. Exploring the ripples of one single case, the programme explores how one mother’s determination to get justice for her daughter would lead to an historic change in the law that has benefitted other families, who had also seen the killers of their loved ones walk free. Catching Britain’s Killers - The Crimes That Changed Us - Wednesday at 9.00pm on BBC Two.