If any "silver bullet" exists it will come out during cross-examination of Cardinal Pell in the child abuse royal commission next week, Broken Rites spokesman Wayne Chamley said.
Cardinal Pell has already given evidence to the commission twice but Dr Chamley noted that was largely about process - the Melbourne Response complaints handling scheme he set up as Melbourne archbishop in 1996 and the "Ellis defence" case as Sydney archbishop.
Cardinal Pell's evidence about any knowledge of pedophile priests during his time in Victoria's Ballarat diocese and as a Melbourne bishop has a much sharper edge on it, Dr Chamley said.
"This is the moment of truth," he told AAP.
"It's beyond belief that he didn't (know). It's just beyond belief."
Dr Chamley said the hearing will be the time for any new documents involving Cardinal Pell to come out.
"There's always been the possibility that some barrister representing someone has got a piece of paper which wasn't captured in the legal discovery process of the commission, and they get him up there and they say `well what about this, isn't this your signature?'.
"That's the silver bullet everybody's hoping for. Whether it exists or not we have to wait and see.
"If that exists then it's open slather in the courts. There's no comeback."
Cardinal Pell has maintained he was never involved in the cover-up of abuse by clergy.
The commission has heard former Ballarat bishop Ronald Mulkearns knew about pedophile priest Gerald Francis Ridsdale from 1975 and moved him between parishes.
But Cardinal Pell, who was one of the bishop's advisers, has said he did not know about the child abuse allegations against Ridsdale.
"It's beyond belief that he didn't (know). It's just beyond belief."
Commission chairman Justice Peter McClellan on Thursday suggested to Bishop Mulkearns that his advisers "knew what was going on" with pedophile priests, but the bishop said he could not recall who knew what at that stage.
A group of abuse victims will be in the Rome hotel conference room when Cardinal Pell testifies via videolink to the commission in Sydney from Monday.
Ballarat survivor Peter Blenkiron said they were not attempting to bring the Catholic Church down nor was it a personal attack on Cardinal Pell.
"It's not a witch-hunt. It's a quest for truth, to protect our children and to support those ones that have been affected," he said.
Helen Last, CEO of clergy victims' advocacy group In Good Faith Foundation, does not expect to hear anything new although Cardinal Pell will be questioned about a number of claims from victims about what they told him.
She said Cardinal Pell had been in key positions in the church hierarchy.
"He certainly had the opportunity to be totally aware of what was going on because of the committees that he was sitting on and the curia and the consultors' bodies," she said.
"He has claimed that nothing was ever talked about, about sexual offending, and that he would not have been involved in moving anyone on. Well that becomes impossible to accept as an answer.
"It's impossible to believe there was never any discussion or naming of pedophilia at all in any of those meetings."
