J, as he is known, is the central figure in Fallen - the first major book on the George Pell court case, written by reporter Lucie Morris-Marr.

Pell was convicted by a 12-member jury in December of sexually abusing J and another 13-year-old choirboy at Melbourne's St Patrick's Cathedral in 1996.

The second victim died after a drug overdose in 2014, but J was able to tell their story to police, a court and the world via the media.

The 78-year-old cardinal was sentenced to jail in March but is now taking the matter to the High Court, having failed to win an appeal.

Morris-Marr says whatever the result of Pell's High Court challenge, J would have made a difference.

"My sources in Rome say, yes, this is being taken very seriously," she told AAP.

"When Pope Francis announced the summit (on clerical sexual abuse) ... he realised if it was seen by the public that he wasn't doing something, it would affect his papacy and legacy.

"So what this choir boy has done - even if Pell ends up winning this High Court challenge - he spoke his truth and it really hurt for him.

"But I think there's a lot more demand in the Catholic community now for change and they can't ignore it.

"This is really smashing down their door now, so it will help others in the future I'm sure."

Morris-Marr says despite changes to child protection policies and professional standards in churches there is still a long way to go, especially on issues such as mandatory reporting of clergy revealing abuse in the confessional.

"Unfortunately the Catholic church attitude is 'We would rather go to jail than break that'."

She says making celibacy voluntary and allowing the greater participation of women would also help, but were being resisted.

"These are traditions in the Catholic church that are very hard to shake."

The Pell case captured the world's attention.

Here was a man considered a possible future pope, one of the most senior figures in the Catholic Church in charge of its finances, on trial for sexual offences.

However, the two trials - the first of which resulted in a hung jury - were veiled in the tightest possible secrecy.

In Fallen, Morris-Marr - the reporter who broke the story in February 2016 - carefully details the saga in a holistic way through to the cardinal's failed appeal in August this year.

But she also reveals the impact on her own life.

She told AAP the publication of her initial story, which was splashed across News Corp tabloids, was like "setting off an earthquake".

It was not just sensational in terms of the claims made in it but the journalist faced a relentless attack from church authorities as well as people within News Corp, which eventually led to her parting ways with the media organisation.

"I was totally perplexed and naturally I was under a lot of pressure and stress," she said.

"I loved the paper ... but in the light of day in terms of what has happened now, I didn't regret it and I now feel with what is going on in the world we have to as journalists keep making everyone accountable, even if it is your own media organisation.

"As journalists we have to have that confidence to represent the public interest at all times."

When the matter eventually went to trial, in frustrating secrecy and harrowing detail, she drew strength from other reporters - known as the "Pell pack" - and their determination for the full story to be told.

"I've made some lifelong friends," she says.

Morris-Marr believes Pell will deny the abuse to the day he dies, fighting the case using a trust fund ("his treasure chest of gold") bolstered by public donations.

"What is really unsavoury about it is right from the beginning he attacked reporters for writing the story, the police, then the jury - and then the choirboy, calling him a liar," she says.

"His team are now attacking high judges of the Victorian appeals court, saying they've made an error of law. Where does it end?

"I feel like he is fighting a losing battle, but it is his right and he will keep going - he has nothing to lose."

Australian Associated Press