PREVIEW: In The Footsteps Of Killers, Channel 4

In this three-part true crime series, Emilia Fox and Professor David Wilson, Britain's leading criminologist, investigate famous unsolved murder cases.

Together they use the latest forensic science and criminological research to shed new light on these troubling crimes and look for new leads that the original investigations may have missed.

Thirteen-year-old David Spencer and eleven-year-old Patrick Warren went missing in Birmingham on Boxing Day in 1996. To this day no one has been charged with the double disappearance and murder of the two friends, and their bodies have never been found despite two major police investigations and a missing persons campaign that featured the boys' pictures on milk cartons.

But now, Emilia and David discover new evidence leading to a prime suspect...

All three episodes of the series are available to watch or download, for free, on All 4, following transmission of this episode, on Wednesday 9 June.