Christopher Dawson is already expected to die in jail for murdering his wife but he has now also been found guilty of having an unlawful relationship with a student.
Judge Sarah Huggett found Dawson guilty of carnal knowledge on Wednesday following a NSW District Court trial of the former rugby league player and teacher.
"F***, f***, f***," Dawson said after the verdict.
The 74-year-old was jailed in 2022 for killing his wife Lynette, last seen in 1982.
A Supreme Court judge found he wanted to pursue an unfettered relationship with a student.
In the latest judge-alone trial, Dawson pleaded not guilty to one count of carnal knowledge as a teacher of a girl over 10 and under 17 years of age, a historical charge replaced in 1986.
His 24-year sentence for murdering Lynette Dawson, whose body has never been found, and laws preventing his parole before it is, mean it's expected he will never be released.
Known at trial as AB, a student in Dawson's year 11 sports coaching class in 1980 said she became engaged in sexual activity with him between July and the end of the school year on December 12.
Public defender Claire Wasley urged the judge to doubt her evidence, particularly around timing.
It was not disputed the pair had a sexual relationship, with Ms Wasley contending AB was mistaken and it began when she was no longer in Dawson's class.
Judge Huggett did find some of AB's testimony had changed over the years and was unreliable but not dishonest and not in relation to her most crucial evidence.
"Those differences are of no particular moment and do not reflect adversely on the complainant," she said.
Her evidence was also "supported by what was seen and heard by other witnesses".
Former students at the Sydney northern beaches school described seeing AB sitting in Dawson’s lap and him standing in between her legs on school grounds and in his office.
AB's colleague at a supermarket recalled a threatening Dawson demanding he stay away from her, the judge finding he perceived the teenager a rival.
A friend described AB disappearing from their social circle in the latter half of 1980, when AB said she was babysitting Dawson’s children and having sexual activity in his car.
The judge found Dawson's Friday night appearances at a pub where students drank underage were not providing support and counsel for AB's domestic issues, as claimed.
He showed up at the pub and told self-aggrandising stories to endear himself.
"Behaviour consistent with a person who on occasion, referred to himself as god," the judge said.
A card Dawson gave AB around Christmas 1980 signed with that name, and another to "the most beautiful girl in the world on her 17th birthday" in 1981 were "powerful evidence" supporting AB's timeline, showing a mature man, confident in the existence of a reciprocal and ongoing relationship which was already sexual, the judge said.
AB said they first engaged in sexual activity at the Maroubra home of Dawson's parents while they were out of town in the latter half of 1980.
The judge was satisfied by AB's evidence and the witnesses supporting it that Dawson was guilty.
He will be sentenced in September.
Outside court, Lynette Dawson's nephew David Jenkins said the verdict had been a long time coming.
“I hope this helps (AB) in her healing and helps her get through what she's had to go through all these years," he said.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
