Darcy John O'Sullivan, or Brother Dominic as he was known, had a reputation among his young male students. The 78-year-old was sentenced on Friday to a maximum of six years in jail for molesting a dozen boys while he was a teacher at Marist Brothers Hamilton (now St. Francis Xavier’s College) and a principal at St Mary's High School in Casino.

O’Sullivan was charged with 22 historic child sex offences which occurred between 1971 and 1983, and there was evidence he may have committed many more.

He was one of three Marist “religious” – along with Brother Patrick and Brother Romuald – whose conduct was examined by the Royal Commission into Institutional Responses to Child Sexual Abuse during its recent Newcastle sitting.

In setting a non-parole period of three years, District Court judge Kate Traill stressed she had to impose a term that reflected the laws at the time the offences were committed. Judge Traill said “the sentence does not represent an appropriate sentence for such offences if committed today”.

The court heard that O'Sullivan opportunistically preyed on boys, sliding his hands over their bodies and into their pants as he walked around the classroom while teaching technical drawing.

He groped the genitals and buttocks of boys who had been sent to his office for punishment, making them sit on his lap or bend over in front of him.

One boy was lying on a stretcher bed in a sick bay, when O'Sullivan entered the room, put his hand under the blanket and touched him on the genitals.

The court heard that O'Sullivan was known to walk around the playground, tucking boy's shirts in and would tell them to "take their hands out of their pockets because they might stray".

One of his young victims started tightening his belt a notch before he went to class. Students tried to barricade the walkway between their desks with stools to prevent O'Sullivan from coming near them.

"We are in for another term of this," one recalled thinking after O'Sullivan had untucked his shirt, rubbed his bare stomach and pushed his hands into his underpants.

Many of the boys O'Sullivan abused were from strict Catholic families and were scared to tell their parents, fearing they would be punished or accused of lying. Some thought this "was just something you had to tolerate" at school, the court heard.

When one victim revealed that O'Sullivan had molested him when he was sent to the principal's office for punishment, his mother said: "You shouldn't be sent to his office in the first place, it's your fault."

The court heard that O'Sullivan had told a psychologist he saw his behaviour as an "outlet of physical affection" rather than for sexual gratification but Judge Trail said that “demonstrates he does not understand the gravity of his offending”.

O'Sullivan will be eligible for parole in August 2019.

In a statement, Marist Brothers Australia apologised to "all those abused" by O'Sullivan.

"What they have endured and the tragic consequences that have flowed from these events are matters of enormous sorrow and regret," the statement said.

"That these crimes should never have happened is without question and we accept that the actions of some of our Brothers has caused great pain and suffering."

The Royal Commission hearings in Newcastle earlier this month heard evidence that O’Sullivan may have preyed on schoolboy Andrew Nash, who took his own life in 1974 at the age of 13. 

There was repeated evidence of the physical and sexual abuse that characterised life for many Marist Brothers pupils at Hamilton and Maitland.

Counsel assisting the commission, Stephen Free, said 32 people had made claims of sexual abuse against one or more Marist brother from schools in the Catholic Diocese of Maitland-Newcastle, including nine people whose claims were against more than one individual.

Francis Cable, known as Brother Romuald, had been the subject of 12 claims, nine of which related to incidents at Marist Brothers Hamilton and Maitland. Cable went to trial in 2015. He is serving a 16-year jail term, with eight years minimum non-parole, over offences relating to 19 complainants.

The commission heard that Thomas Joseph Butler, or Brother Patrick, sexually abused “a large number of boys” in five decades of teaching at Marist schools in NSW and Queensland. He died in 2007 and the Marists apologised for his crimes in 2015 after investigations by the Newcastle Herald.