He was an unhappy, maladjusted child who grew up to be a domestic abuser, an obsessed loner who has a short temper, previous convictions for indecent assault, and a job which allows him considerable freedom to roam the country unobserved. Is this the profile of a potential killer who could be stopped before he strikes?

It sounds like something from the realms of science fiction, but Scotland Yard's new Homicide Prevention Unit (HPU) is studying past murders and murderers in an attempt to thwart future crimes.