Senior Catholic cleric has been in custody in Melbourne since being sentenced in March to six years in prison

On Wednesday the most senior Catholic cleric to be convicted of child sexual abuse, Cardinal George Pell, will find out if his appeal has succeeded and if he will be released from custody.

The 78-year-old has been in Melbourne assessment prison since being sentenced in March to six years in prison for sexually abusing two 13-year-old choirboys in 1996 when he was the archbishop of Melbourne. He was ordered to serve a non-parole period of three years and eight months.

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The jurors heard Pell sexually assaulted the two boys after Sunday solemn mass at St Patrick’s Cathedral in Melbourne in the priest’s sacristy. Pell orally raped one of the boys during this incident and indecently assaulted both of them. Pell offended a second time against one of the boys one month later, when he grabbed the boy’s genitals in a church corridor, once more after Sunday solemn mass. He was convicted on four counts of an indecent act with a child under the age of 16 and one count of sexual penetration with a child under the age of 16.

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Pell’s appeal was heard in June before a full bench of the supreme court including the chief justice, Anne Ferguson, the president of the court of appeal, Chris Maxwell, and Mark Weinberg. Only two of the three judges needs to agree as to whether Pell’s conviction should be overturned.

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Pell’s high-profile appeal barrister Bret Walker appealed Pell’s conviction on three grounds, with the first ground – that the jury was unreasonable in reaching its verdict – the most likely to succeed. However, the unreasonable threshold is a high one to meet. The appellate judges have to find that the jurors must have had a reasonable doubt as to Pell’s guilt, not just that they could have. Walker argued there was a “formidable list” of factors and events that needed to line up for the offending to be possible, and that the jury would have had to believe every one of those factors had occurred. If the judges agree, Pell could walk free from the court on Wednesday.

If Walker fails to convince the court that Pell’s conviction should be overturned on grounds of unreasonableness, he will hope to have succeeded on one of the two other grounds of appeal. One being that Pell was not arraigned in the presence of the jury panel – because there were so many potential jurors, they were split between the main court room and an overflow room with a video link established between the court and jurors. The other being that Pell’s defence team should have been allowed to show a video animation of its argument during the closing address, which the judge presiding over the case, chief justice Peter Kidd, deemed inadmissible. Kidd refused to allow the animation as he said the jurors may view it as factual evidence, and new evidence can not be introduced during closing addresses.

Even if the appellant judges agree that these were errors, they would need to find that the errors were so egregious that they could have affected the jury verdict in order for Pell’s appeal to succeed. If the judges accept the appeal on either of these grounds a retrial would be the most likely result, rather than Pell’s conviction being overturned.

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However, the court may also find it unjust to order Pell to stand trial again, and a permanent stay of proceedings may be ordered which would halt the case from ever continuing. Pell would be released from custody in this scenario. Whether the conviction holds or is overturned, whichever party loses is likely to appeal the decision to the high court. However, there is no guarantee the high court will hear the case, as certain legal requirements need to be met.

In his sentencing remarks Kidd referred to the complainant only as “J” throughout his sentencing remarks, and to the other victim, who died in 2014, as “R” due to protections over their identities.

“During the incident, J and R were crying and sobbing,” Kidd said.

“In my view, the first episode in the priest’s sacristy involved a brazen and forceful sexual attack on the two victims. The acts were sexually graphic. Both victims were visibly and audibly distressed during this offending.

“Your decision to offend was a reasoned, albeit perverted, one. Certainly you were confident your victims would not complain … the offending which the jury has found you have engaged in was, on any view, breathtakingly arrogant.”

The appeal decision will be live streamed on the supreme court of Victoria’s website from 9.30am on Wednesday.