In eight weeks during summer 1986, Michael Lupo, an Italian-born homosexual with sadomasochistic tendencies, strangled four men and tried to murder two others, apparently because he had contracted the HIV virus. He killed because of 'the way my life had worked out and what I had become'.
Like the current investigation, the hunt for Lupo was an undercover, night-time affair, concentrating on London's gay bars, pubs and clubs.
He was trapped when a man who had escaped an attempt on his life volunteered to revisit some of these places, shadowed by plain clothes detectives. Lupo, who worked as a shop assistant in Knightsbridge, pleaded guilty.
Police have the same advantage in this case: their quarry clearly moves within a defined area, both geographically and socially, which is easy to penetrate under cover.
It is possible the killer is extracting revenge after discovering he is HIV- positive. Three of his five victims were discovered to be HIV-positive and the killer might be revisiting partners who could have passed the disease on to him.
Since the mistakes made in the Yorkshire Ripper inquiry and others, detectives have learnt much about recording and cross-referencing information in large inquiries. Computers are now the norm.
The police now also quickly turn to psychologists to build up a description of the quarry by close study of his killing methods.
Professor Robert Blueglass, professor of forensic psychiatry at Birmingham University, said: 'All these cases are distinguished by the fact that these are unusual characters, who behave in an out of the ordinary fashion, but often quite different from that which the police anticipate finding.'
Dr Elliot Leyton, professor of anthropology at the University of Memorial in Newfoundland, Canada, and author of Hunting Humans, a study of serial killers, said 15-20 per cent of such killers were homosexuals.
'It is often not necessary to search for a coherent motive because they do not have one. There are usually bizarre, internalised reasons and when the man is caught, he is unable to be emphatic or specific. Such cases are also marked by increasingly elaborate methods of killing and I would not be surprised to discover an element of torture has been involved.'