the Federal Bureau of Investigation (FBI). FBI career Ressler joined the FBI in 1970 and was recruited into the Behavioral Science Unit, which deals with drawing up psychological profiles of violent offenders, such as rapists and serial killers, who typically select victims at random. Between 1976 and 1979, Ressler helped to organize the interviews of thirty-six incarcerated serial killers in order to find parallels between such criminals' backgrounds and motives. He was also instrumental in setting up Vi-CAP (Violent Criminal Apprehension Program). This consists of a centralized computer database of information on unsolved homicides. Information is gathered from local police forces and cross-referenced with other unsolved killings across the United States. Working on the basis that most serial killers claim similar victims with a standard method (modus operandi) it hopes to spot early on when a killer is carrying out crimes in different jurisdictions. This was primarily a response to the appearance of nomadic killers who committed crimes in different areas. So long as the killer kept on the move, the police forces in each state would be unaware that there were multiple victims and would just be investigating a single homicide each, unaware that other police forces had similar crimes. Vi-CAP would help individual police forces determine if they were hunting for the same perpetrator so that they could share and correlate information with one another, increasing their chances of identifying a suspect. He worked on many cases of serial homicide such as Jeffrey Dahmer, Ted Bundy, Richard Chase and John Joubert, and John Wayne Gacy. Life after retirement Ressler retired from the FBI in 1990 and authored a number of books about serial murder. He actively gave lectures to students and police forces on the subject of criminology and, in 1993, was brought in, in London, to assist in the investigation into the murders committed by Colin Ireland. In 1995, Ressler met South African profiler Micki Pistorius at a conference in Scotland and she invited him to review her investigation of the "ABC Murders", so-called because of their location in the Johannesburg suburbs of Atteridgeville, Boksburg, and Cleveland. A man named David Selepe had died in police custody while being investigated as a suspect for the Cleveland murders, prior to the discovery of the Atteridgeville and Boksburg crimes, and the authorities feared that they had killed an innocent man while the real culprit was still at large. Ressler