David Birnie was the eldest of six children, he was born in 1951. Both of his parents were alcoholics, who spent their money mainly on liquor and had little left over for raising their children. They divorced when he was 10 years old and neither parent wanted custody, so he became a ward of the state. In the 1960s, David was hired at a stable as an apprentice jockey. He was fired after a short time when he approached a female customer wearing nothing but a stocking over his head. As he moved into adolescence, he had already spent time in jail for misdemeanors and felonies. A sex and pornography addict as well as a paraphiliac by adulthood, he had a childless first marriage before his common-law marriage with Catherine.
Catherine was born in 1953. Her mother died before her first birthday and she moved to South Africa with her father. At the age of two she returned to Australia to live with her grandparents and then was sent to live with an aunt and uncle a year later. She was a melancholy sort with few friends. It had even been reported that parents in the neighborhood had forbidden their children to play with her. This cultivated in Catherine a strong need to be loved. She met David Birnie as a child, their families lived next to each other. When she was 15, they began a casual sexual relationship which lasted until her marriage to Donald McLaughlin on her 21st birthday. McLaughlin was the son of the family who had engaged her as a domestic. She had six children with McLaughlin, one of whom died in a car accident as a baby. Shortly after this accident, she abandoned her husband and began living with David. She changed her legal surname to Birnie and became completely dependent on him.
In their late teens, they were engaged in quite a crime spree. In 1969, the two were charged with eleven counts of theft along with breaking and entering. David received 9 months in prison. Catherine was pregnant at the time, so she only got probation. A month later, an additional eight counts of theft were brought before the Supreme Court. David's sentence was increased by an additional three years and Catherine's probation was increased by four years. In July of 1970, David Birnie escaped from prison and reunited with Catherine. Shortly afterward, the couple was arrested again and charged with 53 counts of theft, breaking and entering, trespassing, and illegal operation of a motor vehicle. They had wigs, radios, dynamite, detonators, and fuses, with them when they were apprehended. David was sentenced to two and a half years in prison and this time Catherine had to serve six months of hard time. Her baby was taken by the state.
When released from prison, she was hired as a domestic and fell in love with her employers' son. Their first child was killed after being struck by a car at only 7 months old. Then they had another five children before their marriage began to fall apart. Catherine stopped working around the house and taking care of the family. So she left her husband and children and went back to David.
David required intercourse six times a day to keep him sated. During the time Catherine and David were broken up, David insisted upon intercourse with his brother James, himself a convicted sex offender. James' 21st birthday present from his brother was to sleep with Catherine.