Father John Denham was in his 30s when he raped a 12-year-old boy across a school desk in 1977 and left him bleeding but silenced after threatening to tell the boy's violent father.

Denham targeted boys whose families were stricken by recent tragedy, gave them alcohol and molested them.

He used the school intercom to call victims to his room, fondled boys as they read religious texts in front of class, and molested a boy as he prayed on his knees while in church.

In a Sydney court yesterday Denham, 70, said the word "guilty" 25 times to confirm another 18 victims, only three years after pleading guilty to molesting 39 boys.

Then he was led away to the cells - the "sadistic" priest whose offences against one quiet boy, John Pirona, led to his committing suicide in July last year, aged 45. Mr Pirona's death and the letter he left, in which he spoke of "too much pain", became the catalyst for a federal royal commission into child sexual abuse.

His widow, Tracey, whose two young daughters are only just starting to ask about their father, said she hated her husband's tormentor.

"I feel complete hatred for him [Denham], and the people who knew what he was doing are just as bad," she said.

Another victim, who was caned and screamed at in 1978 when he told St Pius X Adamstown principal Father Tom Brennan that Denham had raped him, said the guilty pleas had come as a relief, even though Denham had already been jailed until 2022 for the earlier convictions.

"He just needs to rot there. I don't want him outside those walls ever again," said the victim, 49, who disclosed his experience to police after a suicide attempt from the top of a church building in 2011.

"It's in my brain, what happened. I'll never forget. Too many people will never forget, and it's why there are so many suicides."

About 60 of Denham's victims have received compensation estimated at $10 million. At least 11 victims have committed suicide.

Most victims have attempted suicide - the first a teenage student in the 1970s while still at the school - and many believe there are possibly several hundred victims.

The victim who was raped with a cane at the age of 12 described St Pius X school in the 1970s as a "brutal and sadistic" place, where Denham used his positions as year master, religious master and priest in residence to gain access to boys.

"The world needs to know what goes on at a Catholic school and the Catholic Church should be ashamed of themselves and be made to pay," the victim said.

Another victim said the guilty pleas provided "some small measure of closure". "He used to say to me 'No one will believe you because I'm a priest'.

"It's been too many years and there's been too many deaths and devastated lives, but finally we've been believed."

Victims thanked Strike Force Georgiana police based at Lake Macquarie for investigations into Denham that started in 2007.

In a short statement yesterday NSW Police noted the result and thanked "the many brave people who came forward and assisted the police".

The matter will return to court in October for sentencing.

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