The reasons George Pell's convictions were quashed

George Pell arrives at Melbourne County Court. File photo / Getty Images

George Pell will be released from prison today after Australia's highest court overturned his conviction for sexually abusing two choir boys.

The former cardinal had spent more than 400 days in Barwon Prison, near the Victorian town of Geelong, after he was convicted of the child sex crimes, alleged to have occurred in the late 90s, in December 2018.

In a statement, the High Court of Australia said there were three main discrepancies in the prosecution's case that led to it quashing Pell's convictions and ordering verdicts of acquittal instead.

The court said those three discrepancies meant it had found it impossible for the jury and Victoria's Court of Appeal to completely exclude any reasonable doubt for the case.

George Pell arrives at Melbourne County Court. File photo / Getty Images

The first was Pell's practice of greeting congregants on or near the Cathedral steps after Sunday solemn Mass.

The second was the established and historical Catholic church practice that required that the applicant, as an archbishop, always be accompanied when robed in the Cathedral.

And finally, opportunity witnesses testified about "the continuous traffic in and out of the priests' sacristy for ten to 15 minutes after the conclusion of the procession that ended Sunday solemn Mass".

The incidents were alleged to have occurred in and near the priests' sacristy at St Patrick's Cathedral in East Melbourne, following the celebration of Sunday solemn Mass.

"The High Court found that the jury, acting rationally on the whole of the evidence, ought to have entertained a doubt as to the applicant's guilt with respect to each of the offences for which he was convicted, and ordered that the convictions be quashed and that verdicts of acquittal be entered in their place," it said.

Even "on the assumption that the jury had assessed the complainant's evidence as thoroughly credible and reliable", the High Court maintained the "opportunity witnesses" used by Pell's defence team put too much doubt into the case.

George Pell arrives at the Supreme Court of Victoria. File photo / Getty Images

Adding: The "unchallenged evidence of the opportunity witnesses was inconsistent with the complainant's account".

The High Court also addressed the majority Court of Appeal decision in 2019, when two of the three judges upheld Pell's conviction.

"Upon the assumption that the jury assessed A's evidence as thoroughly credible and reliable, the issue for the Court of Appeal was whether the compounding improbabilities caused by the unchallenged evidence summarised in (the three reasons above) nonetheless required the jury, acting rationally, to have entertained a doubt as to the applicant's guilt. Plainly they did," the High Court said.

"Making full allowance for the advantages enjoyed by the jury, there is a significant possibility in relation to charges one to four that an innocent person has been convicted."

The High Court also said the honesty of the opportunity witnesses "was never in question", therefore the discrepancies in the case should've been considered by the Court of Appeal.

"The evidence of the opportunity witnesses nonetheless required the jury, acting rationally, to have entertained a reasonable doubt as to (Pell's) guilt in relation to the offences involved in both alleged incidents," the High Court said.

The prosecution alleged Pell's offending occurred on two separate occasions – the first being just before Christmas in 1996 and the second on February 23, 1997.

The victims of the alleged offending were two Cathedral choirboys aged 13 years at the time of the events.

Pell's conviction in December 2018 was the second time the former cardinal had been on trial for the alleged offences.

The jury on the first trial had been unable to agree on their verdicts.

St. Patricks Cathedral, Melbourne. Photo / News Corp Australia