A former St Edmund's College Canberra teacher has been sentenced to eight years behind bars for "predatory and wicked" sex abuse committed against a student in the 1980s.
Garry Leslie Marsh, 72, was found guilty in August of 10 indecent assaults and one act of buggery after he molested the student, then 13, on five separate occasions at his home and in a classroom at the Catholic school.
He has maintained his innocence and sat with his head in his hand as Justice John Burns sentenced him to a non-parole period of four years for the offences in the ACT Supreme Court on Friday.
"These offences involved a gross breach of trust ... You held a position of authority with regard to the victim, which you used in order to gratify your sexual desires," Justice Burns said.
His victim was prompted by the child sex abuse royal commission - which will hand down its final report on Friday - to go to police.
The man who Marsh abused was in court for the sentence. He said in a powerful victim impact statement this week he couldn't stop the "horrible" memories of those crimes "playing over in my mind again, and again, and again".
"I will never forgive you," he said to Marsh. "The taking of my innocence for your own personal pleasure cannot be forgiven".
"I will never forget you or the evil things that you did, and the impact your selfish actions have had over me for my entire life.
"I can only hope that now you will live with the effects of your actions all those years ago for the rest of your life, as do I."
In a letter to parents on Friday, St Edmund's principal Daniel Lawler apologised and expressed "deep sorrow and regret" the boy was a victim of such crimes as a student at the college.
He acknowledged the "distressing and life-long consequences on him of such behaviour".
"We seek to meet such pain with care and compassion, offering that to all who have suffered abuse and the breaking of trust while students at the college."
The court heard the boy considered Marsh "a cool teacher" and the man would sometimes drive him home from football training.
He let him spend time at his house if his mother, who had separated from the child's father, hadn't arrived home.
Marsh would sometimes talk about the boy's sexual development when they were in the car and Marsh would play music at his house and give him food and drink.
Marsh, who was the boy's football coach, first sexually abused the boy when he was kneed in the groin during a match.
He later told him he needed to "check" his injury before he molested him.
On another occasion he called the boy into his classroom and made the child touch him inappropriately.
The boy had later stayed at Marsh's house when his mother was away. He raped the child, causing him to immediately scream in pain.
When the boy went home he told his mother he would never return to Marsh's house. The teacher was later sacked from St Edmund's.
Justice Burns said Marsh had groomed the boy by encouraging him to spend time at his house and his offending involved a degree of premeditation.
He noted the boy showed "clear resistance" when Marsh raped him and had been in "immense and obvious pain".
The judge said Marsh's moral culpability for the offences was very high and he had showed no remorse.
"Your conduct in committing these offences can best be described as predatory and wicked."
The court heard Marsh later taught in Nauru and the Solomon Islands but there was no suggestion he had committed further offences.
Justice Burns acknowledged Marsh was in poor health and acted as primary carer for his elderly mother.
But he said nothing less than an immediate term of imprisonment would be enough to recognise the harm he inflicted on the victim and community.
"Your offending behaviour has had a marked and continuing detrimental effect upon the victim."
Marsh stood slowly in the moments before his sentence was handed down but did not visibly react.
He will be eligible for parole in December 2021.