When the discovery of human flesh blocking the drains of an address in London led to the arrest of 37 year old civil servant Dennis Nilsen, police were staggered when he calmly told them he had killed at least 15 young men. At the time, Nilsen would go down in history as Britain's most prolific serial killer, and as police interviewed the matter-of-fact Scot, they uncovered the extraordinary story of a man obsessed with death since childhood. The lonely job centre executive would strangle his victims and keep their corpses for company, sitting them in chairs, talking to them and watching television together, before butchering burning or boiling the body-parts. Was Dennis Nilsen obsession with death fused during his childhood? Or, was his instinct to kill hard-wired from birth?

• Sue McGregor
• Maria Knowles

• Steve Furst