The gripping series returns with the case of a multi-generation murder in Wales. It took years to bring the killer to justice - had they been hiding within the police's own ranks?

After 19-year-old Cassandra McDermott is found dead in her home, her family endure a cruel waiting game as their only hope for justice is if the murderer tries to kill again.

Stefan Kiszko was convicted of murder when 11-year-old Lesley Molseed was found dead on the Yorkshire Moors. Sixteen years later he was declared innocent, so who did kill Lesley?

On the tenth anniversary of Vikki Thompson's brutal murder in the Thames Valley, a new lead emerges that results in the case being re-opened.

When 77-year-old Georgina Edmonds is murdered in her Hampshire cottage, the community believes the killer must be an outsider, but the police are baffled by a series of dead ends.

The sadistic murder of Wendy Speakes shocked the city of Wakefield, with evidence suggesting that a man with a twisted fetish was on the loose and could kill again.

How it took 14 years to bring Shamsuddin Mahmood's killer to justice.

In 1978, trailblazing scientist Dr Brenda Page was found brutally beaten to death in her Aberdeen home. 40 years later, could a tiny fleck of paint hold the key to catching her killer?

The stories behind famous cold case murder investigations.

Ten years after local Cardiff girl Geraldine's body was found a few days before Christmas, Detective Superintendent Paul Kemp and his team set out to catch the culprit with new groundbreaking forensic science. However, when they get a DNA match to a suspect they must act fast as he is about to be released from Dartmoor Prison.

Thirty years after her murder, could changed loyalties help find Sally McGrath's killer?

In 1979, 22-year-old Teresa de Simone is found murdered in the back of her car. Sean Hodgson is found guilty and sentenced to life but hopes that new DNA technology will clear his name.

Investigating the murder case of Samo Paul and Tracey Turner from the 1990s. In 1997 former Chief constable Mick Creedon and his team in Leicester announced that the cold case murders are the work of one man- a serial sexual predator who is still out there. Creedon uses the DNA in an attempt to catch the killer before he strikes again.

Following the murder case of 26-year-old Surjit Athwal, who failed to come home to London from a family trip to India in the December of 1998. Her husband and mother-in-law returned without her claiming that Surjit changed her travel plans, however Surjit's brother Jagdeesh reported her as a missing person to the police. Law enforcement faced a wall of silence from the tight knit Sikh community. A women who knew what had happened to Surjit feared she would be the next to disappear if she chose to reveal the truth.

Soon after the corpses of two teens were found, a decades-spanning investigation began.

In a nine-year investigation, detectives unpick the disappearance of a 17-year-old-girl.

A woman disappears and an investigation identifies the likely culprit to be her boyfriend.

A mishandled prosecution ended in a murderer going free until new evidence came about.

After a stranger stabs a man to death, authorities spend years piecing together the case.

Detectives encounter a tough case when a mother finds her son's dead body at his home.