Crimes That Shook Britain

In this special episode, we focus on those criminals who have been brought to justice for one crime only to be released to commit further terrible acts. We speak to legal professionals to discover if the system is at fault or have these killers exploited legal loopholes. We talk to victims and family members-if the perpetrators had been kept inside-would their loved ones still be alive?

One of the UK's biggest sex trafficking rings was uncovered in Rochdale in 2012. In a horrific catalogue of abuse, girls as young as 13 were subjected to rape and torture by a gang of nine men. One 15-year-old girl was even 'recruited' by the gang to lure other girls into the trap. After plying them with alcohol and money, the victims would be raped by up to 20 men at a time.

With exclusive, first time access to Dennehy's parents, we hear from the murderer's parents and how the crimes of their daughter have shattered a family. Joanne Dennehy is the first woman in the UK to be handed a whole life tariff by a Judge. Here delve into the mind of such a cold-hearted killer and look at what drove her to become one of Britain's most notorious female criminals.

PC Keith Blakelock was brutally murdered during a riot on a housing estate in North London triggered after a black woman died of heart failure during a house search. Keith received more than 40 injuries during the sustained attack from a number of rioters. Nobody has been brought to justice for his murder to this date, despite three investigations and arrests of more than 300 people.

Peter Tobin is one of the most notorious serial killers in the UK. From 1991 - 2006 he raped and murdered three young girls: Dinah McNicol, Vicky Hamilton, and Angelika Kluk. Yet even prior to these horrific murders he had a history of violence, raping two 14-year-old girls and leaving them for dead. Luckily they survived.

Double murderer, John Sweeney, brutally murdered two of his girlfriends, dismembered their bodies and dumped them in canals. Handed two life sentences he was told he will die in prison. In a macabre twist, a key detective on the case tells how Sweeney allegedly hid clues to his killings in abstract paintings he produced, and how five other girlfriends of his are currently missing as well.