alone after dark. In May 1981 he was sentenced to life imprisonment, and subsequently removed to Broadmoor, a secure hospital for the criminally insane.
The Yorkshire Ripper case taught the police an important lesson. If suspects, like car number plates, had been fed into a computer, Sutcliffe would probably have been taken in for questioning in 1978 – when he was wearing the boots whose imprint was found beside Josephine Whitaker – and three lives would have been saved. A computer would have had no problem storing 150,000 suspects and 22,000 statements.
Yet even with the aid of a computer, the task of tracking down a random serial killer like Sutcliffe would have been enormous. It could only display such details as the methods of known sex offenders, and the names of suspects who had been interviewed more than once. In their next major investigation of a serial killer, the Surrey police began with a list of 4,900 sex offenders – which, as it happened, contained the name of the man they were seeking. The ‘Railway Rapist’ began to operate in 1982; at this stage two men were involved in sexual attacks on five women on or near railway stations. By 1984 one of the men had begun to operate alone. He threatened his victims with a knife, tied their hands, and raped them with a great deal of violence. Twenty-seven such attacks occurred in 1984 and 1985. In January 1986, the body of nineteen-year-old Alison Day was found in the River Lea; she had vanished seventeen days earlier on her way to meet her boyfriend. She had been raped and strangled. In April 1986, fifteen-year-old Maartje Tamboezer, daughter of a Dutch oil executive, was accosted as she took a short cut through woods near Horsley, and dragged off the footpath; she was also raped and strangled. Her attacker was evidently aware of the most recent advance in forensic detection, ‘genetic fingerprinting’, by which a suspect can be identified from the distinctive pattern in the DNA of his body cells. The killer had stuffed a burning paper handkerchief into her vagina. A man who had been seen running for a train soon after the murder was believed to be the rapist, and two million train tickets were examined in an attempt to find one with his fingerprints.
A month later, a twenty-nine-year-old secretary named Anne Lock disappeared on her way home from work; her body was found ten weeks later. Again, an attempt had been made to destroy sperm traces by burning.
It was at this point that the police forces involved in the investigation decided to link computers; the result was the list of 4,900 sex offenders, soon reduced to 1,999. At number 1,594 was a man called John Duffy, charged with raping his ex-wife and attacking her lover with a knife. The computers showed that he had also been arrested on suspicion of loitering near a railway station. (Since the blood group of the Anne Lock strangler had been the same as that of the ‘Railway Rapist’, police had been keeping a watch on railway stations.) Duffy was called in for questioning, and his similarity to the ‘Railway Rapist’ noted. (Duffy was small, ginger-haired and pockmarked.) When the police tried to conduct a second interview, Duffy was in hospital suffering from amnesia, alleging that he had been beaten up by muggers. The hospital authorities declined to allow him to be interviewed. Since he was only one of two thousand suspects, the police did not persist.
At this point, the investigation team decided that an ‘expert’ might be able to help. They asked Dr David Canter, a professor of psychology at the University of Surrey, to review all the evidence. Using techniques similar to those used by the Yorkshire Ripper team – studying the locations of the attacks – he concluded that the ‘centre of gravity’ lay in the North London area, and that the rapist probably lived within three miles of Finchley Road. He also concluded that he had been a semi-skilled worker, and that his relationship with his