In December 1999, a gruesome discovery is made by a police diving team during a training exercise at picturesque Loch Lomond. One by one, limbs from a cadaver are found and brought to the surface. Days later, a severed head washes up on a Scottish beach and is forensically matched to the limbs. They belong to missing 18-year-old Barry Wallace. Police quickly establish a prime suspect, William Beggs - and find that Barry had been handcuffed and sexually assaulted, then dismembered. This documentary takes a forensic look at what happened, and how the killer was brought to justice