For more than a decade after the railway murders, the police knew that John Duffy had not acted alone. The victims had described two men, a short one with ginger hair and a larger one, and Duffy, convicted in 1988, never said who the other was. The name came only in 1998, after years of patient visits by a detective and a course of counseling in prison, when Duffy began making full, detailed admissions and said that every attack had been carried out with his oldest friend, David Mulcahy.
The two had known each other since Haverstock School in north London, where they were once excluded after being found laughing and covered in blood, having beaten a hedgehog to death. In 1982 a woman was raped by two men near Hampstead Heath station. Eighteen more women were attacked over the following year, mostly late at night in dark, quiet places near railway stations in north London, in Hampstead, Barnet and beyond, and there were further attacks in 1984 and three rapes on a single night in 1985 in Hendon. The men called their outings hunting, and before an attack they played Michael Jackson's Thriller loud in the car.
On the evening of December 29, 1985, Alison Day, nineteen, got off a train at Hackney Wick on her way to meet her boyfriend at a trading estate nearby. The two men, who had been driving from station to station, saw her. Duffy threatened her with a knife and both assaulted her, then forced her across live railway lines to the parapet of a bridge. She fell into the canal and swam to the bank, where they pulled her out, took her to waste ground and strangled her with her own blouse. They sank her body in the River Lea with paving setts in her coat pockets. The press name for the attacker changed from the Railway Rapist to the Railway Killer.
On the afternoon of April 17, 1986, Maartje Tamboezer, a fifteen-year-old Dutch schoolgirl, was knocked from her bicycle at West Horsley in Surrey by a wire strung between two trees. She was raped, struck repeatedly on the head with a rock and strangled, and her body was set on fire. A month later, on May 18, Anne Lock, twenty-nine, a secretary at London Weekend Television, was abducted after getting off a train at Brookmans Park in Hertfordshire. Her body was not found for weeks.
Detective Superintendent Charles Farquhar linked the Day murder to the railway rapes, and then to Tamboezer's, when he recognized a belt and a twig in a crime-scene photograph as the parts of a tourniquet ligature. The killings led to Operation Trinity, the first murder inquiry across several forces since the Yorkshire Ripper case and among the first to use computers and an early form of the HOLMES system. The police also brought in David Canter, a psychologist at the University of Surrey, in what was the first use of offender profiling in a British investigation; Duffy later fitted thirteen of his seventeen observations. Duffy, a martial arts enthusiast and former railway carpenter, was arrested in November 1986 while following a woman in a park. Mulcahy was questioned because of their friendship, but the victims could not pick him out at an identity parade and he was released.
At his trial in February 1988 Duffy was convicted of the murders of Day and Tamboezer and four rapes, and acquitted of raping and killing Anne Lock. He was given a minimum of thirty years, later raised to a whole life term by the Home Secretary. When he finally talked in 1998, he was interviewed under caution for a week at a remote Hertfordshire police station, around the World Cup games he asked not to miss, and he described the three murders, including what had happened to Lock, and how the pair had grown skilled at approaching and controlling their victims. In March 1999 he pleaded guilty at the Old Bailey to seventeen offenses of rape and conspiracy to rape, all committed, he said, with Mulcahy.
Mulcahy was watched for several months and arrested on February 6, 1999. DNA testing, not available in the original inquiry, tied him to the crimes, and a search of his home turned up the Thriller tape. He answered no questions in interview. Since Duffy's conviction he had been convicted of assault occasioning actual bodily harm for beating one of his sons and given a non-custodial sentence. Before the trial, letters from his defense team reached prisoners on Duffy's wing telling them Duffy was the main witness against him, and the prison had to move to protect Duffy; the solicitors blamed a clerical error.
The trial opened in Court No. 1 at the Old Bailey on September 11, 2000, before the Recorder of London, Michael Hyam. Duffy gave evidence against him over fourteen days, the first time a Category A prisoner had testified against an accomplice, and the prosecution presented Mulcahy as the leader, the one who decided that rape was no longer thrill enough and that the women should die. In the witness box Mulcahy denied everything, said Duffy was lying and the police had planted the DNA, and accused the detective Les Bolland of coaching Duffy. In February 2001 he was convicted of three murders and seven rapes and given three life sentences with a recommendation of thirty years, and twenty-four years for each rape. Weeks later Duffy received twelve years for each of seven rapes he had admitted. A website in Mulcahy's name has argued his innocence and sought a retrial.