Australian Cardinal George Pell has applied to attend the Victoria state Court of Appeal in Melbourne in person for the challenge that is set to be heard by three judges on Wednesday and Thursday.
But he is not required to come to court and could remain in the Melbourne prison where he has been held in custody since he was sentenced in March to six years in prison. He is held in special protective custody because paedophiles are regarded as being at higher risk of harm from other prisoners.
Pope Francis's former finance minister was convicted in December of orally raping a 13-year-old choirboy and indecently dealing with the boy and the boy's 13-year-old friend in the 1990s. Pell had become archbishop of Melbourne, Australia's second-largest city, only months before.
Court orders had prevented publication for months of the details of that trial and an earlier trial on similar charges that had ended in September with a deadlocked jury.
Pell was initially spared prison when he was convicted so that he could have both knees surgically replaced at a Sydney hospital.
Professor Jeremy Gans, who heads the Melbourne Law School and is an expert on Victoria criminal law, said Pell has a strong chance of winning the appeal on the ground that the verdicts were "unreasonable".
Pell's lawyers will argue that the jury could not have been satisfied beyond reasonable doubt that Pell was guilty based on the word of the surviving victim against "unchallenged exculpatory evidence" of more than 20 prosecution witnesses.
One of Pell's victims died of a heroin overdose in 2014 at the age of 31, apparently without making any accusation of abuse. State law prevents victims of sexual assault from being publicly identified.
If the appeal judges rule that the verdict is unsafe on the evidence, Pell would by acquitted and would not have to be retried. But prof Gans suspects the case could end up in the High Court, Australia's final appeals court.
He said: "I think he's likely to win on the unsafe verdict ground. I'm sure whoever loses in the Court of Appeal is going to try to appeal in the High Court. Once it gets to the High Court, things get really unpredictable. They're the least predictable court in Australia."
Pell's lawyers have also said they will argue that the trial judge erred in not allowing them to use a video graphic in their closing address. They said the graphic would demonstrate that the crimes that were alleged would have been impossible.
A third ground details an alleged "fundamental irregularity" in the trial in that Pell was not arraigned - asked if he pleaded guilty or not guilty - in front of the chosen jury.
A victory on either of those grounds could result in Pell being retried. But he would likely be freed on bail until his third trial.
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