In December 1999, a grim discovery is made during a routine police diving exercise in the bitterly cold waters of Loch Lomond.

Divers spot submerged bin bags, expecting them to be filled with rubbish - but upon closer inspection they instead find human limbs. Eight days later another bag - containing a head - is found washed up 60 miles away on Barassie Beach, Ayrshire.

This series tells the inside story of the investigation into a crime which shocked the country. Senior police officers, including detectives at the heart of the inquiry, experts and crime journalists give their insights into a horrific murder and the pursuit of justice.