By the time of his third marriage, it has been established that he had already claimed his first victim, 10-year-old Jack Blake, a neighbour’s child, on 7 April 1972. Shawcross had taken him fishing just a few days before he disappeared but denied any knowledge of the disappearance, and it was five months before the boy’s body was finally located. He had been sexually assaulted and suffocated.
In September 1972, the body of eight-year-old Karen Ann Hill was found under a bridge. She had been raped and murdered. Mud, leaves and other debris had been forced down her throat and inside her clothing. Neighbours remembered that Shawcross had been seen with Karen in the vicinity of the bridge before her disappearance and Shawcross, who had a history of minor run-ins with local children, came under immediate suspicion.
He was arrested on 3 October 1972, and finally confessed to both killings, although he was only charged with Karen Hill’s murder, given the lack of evidence tying him to Jack Blake’s death. He received a 25-year jail sentence and third wife Penny divorced him shortly thereafter.
After serving less than 15 years of this sentence, he was released on parole in April 1987. The well-publicised resettlement of a child killer in the Binghamton area of New York State was greeted by a public outcry and he was forced to leave the area after a few months, along with his new girlfriend, Rose Whalley. His criminal record meant that he would be unwelcome almost anywhere, and the authorities made the decision to seal it, to prevent a recurrence of the public alarm in Binghamton, before moving Shawcross and Whalley to Rochester, New York, where she became his fourth wife.
In Rochester, Shawcross took on a succession of menial jobs, and his lacklustre marriage to Whalley meant that he was soon seeking solace elsewhere, both from prostitutes and his new girlfriend, Clara Neal.
It did not take long for Shawcross to return to his murderous ways. Whether he made a conscious decision to target prostitutes, whose disappearance might not cause as much of an outcry as children, or whether the women taunted him for his sexual inadequacies, as he later claimed, was never clear. His first victim was discovered by hunters on 24 March 1988. She was 27-year-old prostitute Dorothy Blackburn, and her body was found in the Genessee River, dumped there following a vicious attack, which included bite marks in the groin area and strangulation.
With little evidence and no public impetus to solve the murder of a prostitute, her case languished for over a year. There were other murders of prostitutes in that time but, given the danger of the profession, nothing untoward was noticed that linked any of the cases, until the discovery of the body of another prostitute, Anna Steffen, on 9 September 1989. She had also died of asphyxia and her body had been dumped in a similar way to that of first victim, Blackburn. However, her body was found far from the original murder scene, so once again the possibility that a serial killer was at work was not recognised by police investigators.
On 21 October 1989, the body of a homeless woman, Dorothy Keeler, 59, was discovered, followed six days later by another prostitute, Patricia Ives, in the same area. Both women had been asphyxiated and the press started to show an interest as the cases were linked, coining the term 'The Genessee River Killer'. In all cases, at least some attempt at concealment had been made, which police felt indicated previous criminal or military experience. They began to advise prostitutes working in the area to exercise caution, and sought as much information as possible about strangers operating in the area, as well as checking criminal records for offenders who might be living in the immediate area. Shawcross’ sealed criminal record meant that he escaped police attention at the time.
As prostitutes continued to disappear, it became apparent that the killer must be someone familiar to the women who worked in the area, and police were able to piece together a description from a number of women of a regular punter called 'Mitch' or 'Mike', who was prone to violence.
The body of 26-year-old June Stott, who was neither a prostitute nor a drug user, was found on Thanksgiving Day. She had been strangled, anally mutilated after death, had her labia removed and was gutted from throat to crotch like a wild animal.
With the body count mounting, the police sought assistance from FBI profilers, who divided the 11 unsolved prostitute murders into sub-groups according to method and position. They developed a profile that described the killer as a white male in his 20s to 30s, strong, probably with a previous criminal record, familiar with the local area, and comfortable enough with the victims that they would enter his vehicle without question; to all outward appearances a 'regular guy'. The lack of sexual interference indicated it might be someone with sexual dysfunction. The post-mortem injury inflicted on June Stott, and not on any other victim, indicated that the killer was becoming more comfortable around corpses, probably returning to the crime scene again later to relive the attack.
The discovery of the body of Elizabeth Gibson, on 27 November, brought a breakthrough. Suspect 'Mitch' had been seen with her shortly before her disappearance but they seemed no closer to establishing his identity. Police tried various tactics, including canvassing all the local bars, to no avail.