As of 2007, Dupas has been convicted of three murders and is a prime suspect in at least three other murders committed in the vicinity of the Melbourne area during the 1980s and 1990s.
Dupas was born the youngest of three children into what has been described as "a fairly normal family". Born in Sydney, New South Wales, his family moved to Melbourne while he was still a toddler. With both siblings considerably older, his parents treated him much like an only child. Dupas left high school upon completing Form 5, and later obtained his Higher School Certificate while in custody.
On October 3, 1968, at the age of 15, Dupas, still attending high school at Waverley High School in the eastern Melbourne suburb of Mount Waverley, visited his next door neighbour requesting to borrow a knife for the purpose of peeling vegetables. Dupas was apprehended after he stabbed the woman in the face, neck and hand as she attempted to fight off his attack. He later told police he could not help himself and did not know why he began to attack the woman. He was placed on 18 months probation and admitted to the Larundel Psychiatric Hospital for evaluation; he was released after one day and treated as an outpatient.
In October 1969, a mortuary located at the Austin Hospital was broken into. The bodies of two elderly women were mutilated using a pathologist's knife. One body contained a strange wound inflicted with a knife to the area of the thigh. Police now believe Dupas was involved in the break-in as the wounds inflicted matched that of a later murder victim, Nicole Patterson.
Senior Detective Ian Armstrong, who interviewed Dupas on November 30, 1973, at the Nunawading Police Station described Dupas as "weak and compliant" when confronted by authority.
"He stood out. To me the guy was just pure evil … His attacks were all carefully planned and he showed no remorse. We could see where he was going. I remember thinking, 'This guy could go all the way'. He is an unmitigated liar … he is a very dangerous young person who will continue to offend where females are concerned and will possibly cause the death of one of his victims if he is not straightened out."
After Dupas received a term of nine years imprisonment for rape in 1974, prison psychiatrist Dr. Allen Bartholomew noted Dupas was in constant denial of his criminal activity, noting at the time: "I am reasonably certain that this youth has a serious psychosexual problem, that he is using the technique of denial as a coping device and that he is to be seen as potentially dangerous. The denial technique makes for huge difficulty in treatment."
On July 25, 1974, Dupas was sentenced to nine years imprisonment with a minimum period of five years for an attack on a married woman in her own home. Dupas broke into the victim's house and threatened her with a knife before tying her up with cord and raping her. He threatened to harm her baby when she resisted his attack. The sentencing judge described the offence as "one of the worst rapes that could be imagined".
In 1979, approximately two months after his release from prison, Dupas again molested women in four separate attacks over a 10 day period. On February 28, 1980, Dupas received a five year minimum prison sentence for three charges of assault with intent to rape, malicious wounding, assault with intent to rob, and indecent assault. A 1980 report on Dupas stated "There is little that can be said in Dupas' favour. He remains an extremely disturbed, immature and dangerous man. His release on parole was a mistake."
Dupas was again released from prison in February 1985. Approximately one month later, he raped a 21-year-old woman on a beach at Blairgowrie. After alighting from his car, Dupas followed the woman and attacked her, holding her to the ground at knifepoint before raping her. He later told police: "I'm sorry for what happened. Everyone was telling me I'm OK now. I never thought it was going to happen again. I only wanted to live a normal life."
On June 28, 1985, Dupas was sentenced to 12 years imprisonment for the Blairgowrie rape, and released in 1992 after serving seven years of his sentence.
Less than two years after his release from prison, Dupas was arrested on charges of false imprisonment over an incident at Lake Eppalock in January 1994. Wearing a hood and armed with a knife, insulation tape and handcuffs, Dupas followed a woman who was picnicking and held her at knifepoint in a toilet block. On August 18, 1994, after entering a guilty plea to one count of false imprisonment in the Country Court in Bendigo, Dupas was sentenced to three years and nine months imprisonment, with a minimum period of two years and nine months. In September 1996, Dupas was again released from prison and moved into a house in the Melbourne suburb of Pascoe Vale.
While imprisoned at Melbourne's Pentridge Prison, Dupas formed a relationship with mental health nurse Grace McConnell, who was 16 years his senior. The pair married in 1987 inside Castlemaine Gaol.
McConnell described her marriage to Dupas during the inquest into the murder of Mersina Halvagis:
"He insisted that he was in love with me .... and that with my help he could come out of himself and become a normal person. I agreed (to marry Dupas), not out of particular love for this man but from a sense of responsibility to helping him become a useful member of the community. In my mind, our relationship was mother and son. "Our sex life was very basic, almost non-existent. I would go along with it out of a sense of responsibility … It got to the stage where I could not bear him touching me.
His new wife found him to be a self-obsessed, lazy, needy, and a snob, and they divorced during the mid 1990s
As of 2006, Dupas is serving his sentences between the maximum security protection unit of Port Phillip Correctional Centre, at Laverton and HM Prison Barwon in Lara, a northern suburb of Geelong. He has attempted suicide several times while imprisoned. Prison staff describe him as a model prisoner while in custody and "a monster" whenever released.
Before his first conviction for murder, Dupas had 16 prior convictions involving acts of sexual violence from six court appearances between March 27, 1972 and November 11, 1994.