As a former local detective of 20 years, Matt Casey also says some evidence given in the Pell case may not be "safe" on appeal.

Mr Casey said he respected the jury's verdict. "I'm not saying it didn't happen … I feel sorry for the victims, but there is room for caution and I await the appeal with interest," he said.

Pell was sentenced to six years' prison with a non-parole period of three years, eight months by Judge Peter Kidd in Melbourne Victorian County Court on Wednesday morning.

He was convicted of one count of sexual penetration of a child under 16 and four counts of indecent acts on two boys committed 20 years ago while Archbishop of Melbourne.

Judge Kidd described the acts as "brazen and opportunistic," committed by a man who was well aware of his authority within the church.

Despite the absence of pre-planning in the offences, Judge Kidd said Pell's authority carried a "significant responsibility" not to do anything to the children's detriment.

Mr Casey is a former director of the Institute for Professional Standards and Safeguarding, established by Archbishop Christopher Prowse in 2015 in the wake of the Royal Commission into Institutional Responses to Child Sexual Abuse.

He retired from this role, which involved investigation and referral of complaints, in August 2017.

He has watched the Pell case closely from several perspectives.

"I've dealt with hundreds of victims and I think, in my whole experience, I've never seen anyone come forward who was completely making something up," he said.

While he never believed anyone was lying, Mr Casey said in some cases the person the accuser nominated did not turn out to be the abuser, which he attributed to memory over the passage of time.

"I didn't sit through the Pell evidence, but from what I've heard, I find it hard to believe it was this person (Pell)," he said.

Mr Casey said he had great faith in the legal system, but he was also troubled by his own experience with cases in which he believed the outcome was a "lay-down misere," yet the jury returned a not guilty verdict. Other times, it worked in reverse.

He cited the fact that one of Pell's victims died before the case. It's understood the man had never made a complaint to the Church, and denied being abused when asked by his mother.

Mr Casey is a regular churchgoer, but says his faith is not shaken by Pell's conviction and sentencing.

"One of the best bits of advice I ever received was from my father, who said 'Don't let the church get in the way of your faith'," he said.

"My faith is rock solid, even though I recognise there are some significant issues to be addressed in Australia and throughout the world … It's a failure of leadership, but I have been impressed by Christopher Prowse because he's trying to respond."

In his five and a half years working in ethics and professional standards with the Archdiocese, Mr Casey said Archbishops Mark Coleridge and Christopher Prowse made a "genuine commitment" to making the necessary changes.

"I wouldn't have stayed if I didn't see that commitment," he said.

His brother, Danny Casey, was appointed by Pell as business manager of the Sydney Archdiocese. He also went on to become project leader for the reforms Pell initiated in the Vatican's treasury, following the discovery of corruption and criminality.

While Matt Casey had met Pell, who was also a friend of his brother's, he said his comments were driven by his knowledge of the legal system, and not familial loyalty.

"If he (Pell) did it, it's reprehensible and a great betrayal of everything. If he didn't do it, it's also awful. There is no middle ground," he said.

Meantime, Archbishop of Canberra-Goulburn Christopher Prowse has acknowledged that Pell's conviction and sentencing has "profoundly disturbed the Catholic community in the Archdiocese".

The Archbishop declined to answer detailed questions, but issued the following statement on Wednesday morning.

"Given Cardinal Pell’s appeal of this decision, further comments on the matter from the Archdiocese will not be given.

"Once again, we commit ourselves to standing alongside all survivors of sex abuse. We continue in ensuring child safe environments in all we do.

"All of this is taking place during the penitential liturgical season of Lent. We find ourselves at a fresh Calvary. We wait in faith and hope for the dawn of Easter."

In February, when the suppression order on Pell's conviction was lifted, Archbishop Prowse also declined detailed comment, given the impending appeal.

But he said the revelations had "deeply shocked and disturbed us".

"We find in our hearts so many emotions and confusions," he said.

"We hold deeply in our hearts all survivors of sex abuse and their families. We pledge to do all we can to stand alongside them in prayerful, transparent vigilance."

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