During form 5, he left the horrors of school and took up an apprenticeship as a fitter and turner at General Electric in nearby Notting Hill. As is the case with a lot of socially unacceptable serial sex offenders who get their kicks out of dominating and dehumanizing defenseless women, while doing his apprenticeship Dupas, applied to join the police force so he could exert his authority legally. But he was rejected for being 1cm too short.
On March 10, 1972, a man chased and caught 19-year-old Dupas after finding him peeping through the bathroom window at his wife in the shower. On November 15, 1973, Dupas was interviewed by police after a motorist reported that he had repeatedly driven alongside the complainant's car, staring and smiling at his 12-year-old daughter.
Two weeks later, detectives from nearby Nunawading arrested and charged Dupas with the rape of a married woman three weeks earlier on November 5, 1973. They alleged that Dupas had asked his victim for help claiming his car had broken down outside her home. While the woman was looking for a screwdriver, Dupas hid in the house then threatened the woman and her 18-month-old baby with a knife before raping her.
Police alleged that in the two weeks before he was picked up, Dupas had tricked his way into two homes with the same ruse, but had left without assaulting either woman. He stole money from the first house and left, and fled from the second when the woman told him her husband was on the way home and would be there any minute.
Even in those early days, arresting detectives saw the potential danger in Dupas and the leader of the investigation, Senior Sergeant Ian Armstrong, described him to reporters as "an evil, cold, baby-faced liar who would possibly cause the death of one of his victims if he wasn't straightened out."
The investigating detectives discovered that Dupas was a consummate liar and a frustrating interview subject, as even in the face of overwhelming evidence he would deny everything. Then he would break down, and just when it looked as though he was about to make a confession, he would straighten himself up and deny everything again and they would have to go back and start again from the beginning.
Detectives also discovered that Dupas was no ordinary rapist who chose his victims at random. He was organized to the point where he had everything worked out down to the last detail. He had pre-chosen his victim(s) and went about his business in a very cold and calculated fashion, remaining calm at all times, even when arrested.
"He was a cool, cunning liar," Detective Armstrong told reporters. "You'd look at him and think, 'Could he be this callous, this dangerous? But I knew this guy would be a danger...you could smell it.'"
After being charged with rape and released on bail, Dupas was remanded to Mont Park psychiatric hospital, where he was allowed to come and go as he pleased. While still attending Mont Park, Dupas was arrested for a series of incidents at nearby Rosebud Beach.
He was seen on at least three occasions entering a female toilet and shower block and watching girls showering before he was trapped in a police stakeout. Dupas was taken back to Mont Park and admitted as a voluntary patient, where he stayed put from January 8 to February 22, 1974.