During the late 1980s, the police mounted one of the biggest manhunts in British criminal history in search of 'the Railway Rapist'. It was later discovered that the rapist was working with an accomplice, and after the first murder, the pair became known as ‘the Railway Killers’.

John Duffy was a brutal rapist and killer who struck lone women at railway stations throughout the South East and mainly North and West London. He was at first thought to have carried out his heinous crimes alone and was sentenced to life imprisonment for the murders. However, police were sure that he had an accomplice.
Only after 15 years did the advance of forensic science allow them to arrest David Mulcahy, a childhood friend of Duffy, who was eventually convicted. This case saw the first use in Britain of 'Psychological Offender Profiling'.
However, Mulcahy still protests his innocence after stating that Duffy implicated him in the murders.

John Duffy and David Mulcahy had been lifelong friends since their days together at school in Haverstock, north London. They both shared an early sadistic streak for tormenting and torturing animals starting with a hedgehog, which Mulcahy beat to death with a plank when he was aged just thirteen.
As they got older the boys began to transfer their sadistic tendencies to women, fuelling each other’s dark sexual fantasies. The pair, both building workers from Hampstead, most likely got the idea to attack lone women when they realised how quiet areas were around railway stations at night.
It is baffling to understand how a young friendship could have degenerated into a secret life of violence, rape and murder. One theory is that bullying, which both Mulcahy and Duffy endured as schoolboys, may have been a key factor in driving them to rape and kill.
Whatever the trigger, the two boys had developed a severely psychotic side to their personalities at an early age. As he grew older, Duffy married and became a martial arts fanatic.
Their brutal crimes began on 1 July 1982, when the pair attacked and violently raped a 23-year-old woman in Hampstead, North London. Over the next four years, a further 18 women were attacked.
Despite John Duffy being known to the police as a violent man - after assaulting his wife and being found carrying a knife - he was still able to carry out a string of sexual assaults and commit two murders over a 15-month period.