Behind bars in Britain are some of the most dangerous people the country has ever known.
Killers – men and women - who have killed and killed again to satisfy their own dark desires, often targeting the most vulnerable members of our society.
But who is the worst of the worst? Can we create an index of evil?
Criminologist, Professor David Wilson, has developed a unique system that he believes can Measure Evil, and by doing so, countdown to reveal just who is the most dangerous killer alive in Britain today.