This episode travels to Edinburgh to look at the fascinating story behind one of Scotland’s longest-running investigations, the World’s End murders, a double murder from 1977.

Back then, forensic science was still in its infancy, and a lack of evidence meant that for nearly 40 years the killer went free - until a modern day expert witness unlocked clues hidden in some soil samples and helped convict the murderer.

Our second investigation starts on Scammonden moor, near Huddersfield, and looks at the science behind the capture of the killer of Christopher Pratt.

Of all the evidence gathered at the scene of a crime, perhaps some of the most surprising is the tiny creatures who act as silent witnesses to the events that unfolded. Insect life can help prove a timeline right at the beginning of an investigation when clues are thin on the ground, and this case shows just how crucial this evidence can be. Show less