Reading from his victim impact statement at the Downing Centre court on Friday the one time altar boy, now grown up, struggled to control his emotions as he told how the assault had ruined his life.

"I heard the names of these so-called leaders during the trial, namely Cardinal James Freeman and Bishop Edward Kelly," he said. "I never had any contact with them but their decisions have impacted on my life," he said.

"[They] knew that he had sexually abused a young boy and all they did was move him from parish to parish to give him new young boys to manipulate and abuse without having any restraints put on him.

"Instead they promoted him to being youth leader and parish priest to make it easier for him to get into situations where he would be left alone in one-to-one contact with young boys."

Father Robert Flaherty, aged 72, sat in the dock with both hands resting on the handle of a walking stick but showed no reaction to the statement or that of a second victim read on his behalf by his sister.

He had pleaded guilty to three offences of indecent assault but was also found guilty by a jury of two similar offences in September. Some of the offences took place at the priest's Mollymook weekender where he allowed the victim's sister to sleep in his bed in case any of the boys made advances towards her. He, instead, slept in the boys' room. That was something that took "a degree of planning and was something that was arranged", prosecuting counsel Mitchell Paish said.

The first victim added: "We fed a few kookaburras down at his holiday house but now, it doesn't matter what mood I am in, when I see a kookaburra the shame and guilt and anger rise to the surface."

The assaults took place during the 1970s but Flaherty was only arrested in 2013 after a third victim complained to police shortly after the announcement of a royal commission into child sex abuse.

Flaherty, from Wentworth Falls in the Blue Mountains, held positions at Our Lady of the Rosary Church in St Marys, churches in Guildford, Woy Woy and Auburn as well as at St Patrick's Church, Blacktown and St Monica's Church, Richmond.

Mr Paish​ told the sentencing hearing that the offences were so serious that nothing other than a full custodial sentence should be considered.

"Even now this man fails to realise the hurt and misery he has caused long term in people's lives," he said.

Defence counsel Leah Rowan said a doctor last September gave Flaherty, reportedly suffering from dementia, depression and diabetes, six to 12 months to live and that a custodial sentence would hasten his demise.

"That in my submission means that any full-time custodial sentence your honour may impose would almost certainly be a death sentence," she said.

Judge Richard Cogswell SC interjected saying: "Or a life sentence."

Mr Paish, prosecuting, added: "Mr Flaherty may be around in five years time."

Sentencing will take place on Thursday.

National Sexual Assault, Domestic Family Violence Counselling Service 1800 RESPECT (1800 737 732).