Mulcahy was born in 1959 and had been a friend of John Duffy since primary school in north London. Both were small men, and they attacked together, using martial arts and knives, calling their expeditions hunting.
From 1982 they raped women near railway and Underground stations across London and the south-east, and the number of attacks attributed to the pair runs into the dozens. Three women were killed: Alison Day, nineteen, at Hackney Wick in December 1985; Maartje Tamboezer, fifteen, at East Horsley in April 1986; and Anne Lock, twenty-nine, at Brookmans Park in May 1986. The press called the unknown attacker the Railway Rapist and then the Railway Killer.
The investigation was the first in Britain to use a psychological profile: David Canter, then at the University of Surrey, was asked to analyse the geography and sequence of the attacks, and produced a description that matched Duffy closely enough to move him up a list of nearly two thousand suspects. Duffy was arrested in 1986 and convicted in February 1988 of two murders and five rapes.
Duffy had always worked with someone and would not say who. He served eleven years, then in 1997, in therapy in prison, named Mulcahy and gave a detailed account of their offending together. Mulcahy was arrested in 1998.
He was convicted at the Old Bailey on February 2, 2001 of three murders and seven rapes and sentenced to three life terms with a recommendation of at least thirty years. Duffy was convicted at the same trial of the third murder and further rapes. Mulcahy has always denied everything and his appeals have failed.
The conviction rests substantially on Duffy's evidence, given a decade later by a man already serving life, together with forensic material re-examined in the 1990s. The entry records both the profiling history, which is why the case is significant in British policing, and the nature of the evidence against Mulcahy.