John Sidney Denham used his position as a parish priest and a teacher at St Pius X Catholic School at Adamstown to repeatedly assault, rape or molest at least 57 young boys without interruption for 18 years.

In the Downing Centre District Court on Friday the 73-year-old was sentenced for 48 of these offences, having already been sentenced to at least 13 years' jail for the other nine offences.

With a partial accumulation of the sentences he now will spend 19 years and five months behind bars.

"Some of the offences represent the most abhorrent and sadistic combination of circumstances that courts are likely to see," Judge Helen Syme said of the abuse as Denham sat in the dock with his head bowed.

As a number of the former priest's victims sat crying in court, Judge Syme described how, between 1968 and 1986, Denham would target young students from St Pius who came from difficult or disadvantaged backgrounds.

"The complainants were from devout Catholic families who…were required to attend school or church chosen by their parents and required to honour their priests and teachers," Judge Syme said.

"As a result they became easy prey for the offender who had to do little to gain their trust," she said.

He would then use his position to "groom" the boys and their parents, before preying on the children over and over again.

The attacks took place in Denham's office, in classrooms, outside confessional boxes, and sometimes in public places such as the playground, and ranged from touching the boy's genitals over their clothes to brutal, sadistic rapes.

Denham appeared to enjoy the pain he was inflicting, often caning the boys after sexually abusing them and then threatening further punishment if they dared to complain.

"On many occasions the offender threatened the children with further physical harm or exposure to the school community as a homosexual if they complained," Judge Syme said.

"…the offender knew any complaints would be fruitless and he occasionally taunted the children with this knowledge…saying, on one occasion, 'if you want to tell someone, tell God'."

Judge Syme also found that Denham had been protected and even encouraged in his sexual offending by the headmaster of St Pius at the time, Father Tom Brenan, and by Father Ron Picken, a priest at the neighbouring Wingham parish.

She found that Father Brennan, now deceased, had been told numerous times about Denham's "depraved behaviour" by some of the boys and their parents, but continued to send students to the paedophile's room where they were subsequently abused.

Judge Syme referred to a number of incidents in which Denham and Father Picken gave the boys alcohol during trips to the latter's parish at Wingham, and that the latter was "generally present" when the abuse was occurring during these trips.

"There is no other plausible explanation other than that the other priest knew what was occurring," she said.

Judge Syme said that while the impact of Denham's abuse on his victims had been "catastrophic", he showed no remorse, but rather saw himself as a "martyr", complaining about the absence of intelligent people in jail with whom to converse about history and moral philosophy.

She did not find that the time which had elapsed since the offending gave Denham any entitlement to a more lenient sentence, declaring "old sins cast long shadows".

Denham was given a maximum 19-year sentence, with a minimum of 13 years.

With a partial six-year accumulation of this sentence with the sentence he is already serving, Denham will be eligible for release no earlier than January 2028, when he will be 85 years of age.