CANBERRA, Australia (AP) — The most senior Catholic to be convicted of child sex abuse took his appeal to Australia’s highest court Wednesday in potentially his last bid to clear his name.

Cardinal George Pell was sentenced a year ago to six years in prison for molesting two 13-year-old choirboys in Melbourne’s St. Patrick’s Cathedral while he was the city’s archbishop in the late 1990s.

His lawyers argued in the High Court that an apparently truthful victim was not enough to dispel reasonable doubt about guilt. The seven judges will hear the prosecution case on Thursday on why the convictions should stand.

Pell was convicted by the unanimous verdict of a Victoria state County Court jury in December 2018 after a jury in an earlier trial was deadlocked. A Victoria Court of Appeal rejected his appeal against his convictions in a 2-1 majority decision in August last year.

Pope Francis’ 78-year-old former finance minister argued before the High Court that the guilty verdicts were unreasonable and could not be supported by the whole of the evidence from more than 20 prosecution witnesses who include priests, altar servers and former choirboys.

Pell's lawyer Bret Walker told the judges that there had been a “reversal of onus” in which Pell was expected to prove the offending didn't happen instead of prosecutors proving the crimes were committed beyond reasonable doubt.

“That is a wrong question which sends the inquiry onto a terribly damaging wrong route,” Walker said.

“Impossible was not something we had to prove, but if we showed it, then obviously there's a reasonable doubt,” he added.

Walker said the evidence of a former choirboy, now aged in his 30s with a young family, was the only evidence that Pell had committed the crimes.

Walker said the allegations that Pell had molested the two boys in a priests' sacristy moments after a Mass could not be proved if the jury had accepted the evidence of sacristan Maxwell Potter and Monsignor Charles Portelli.

Potter had testified that the sacristy was kept locked during Masses and Portelli had given evidence that he was always with Pell while he was dressed in his archbishop's robes.

Walker said Pell did not have a five or six minute opportunity required to molest the boys in the sacristy before altar servers and clerics walked in.

“Unlike so many appalling historic sexual misconduct cases, the alleged offending had taken place in a milieu quite different from the usual secluded, secretive or completely private setting,” Walker said.

Prosecutors have told the judges in written submissions that it is not their role to determine whether it was open to the jury to find the offending behavior proven beyond reasonable doubt.

Outside court, Pell supporters clashed with a man from a victims advocacy group. Michael Advocate from Victim Justice held signs saying, “Burn in hell Pell.”

A group of Pell supporters tried to block Advocate from speaking to reporters, yelling for Pell to be forgiven.

The group of about 50 supporters, many holding Australian flags, sang hymns outside of the court as lawyers prepared for the case inside.

The court will effectively hear Pell’s appeal in its entirety before they technically decide whether they will even hear his appeal.

They could decide he does not have permission to appeal, he has permission to appeal but the appeal is denied, or he has permission to appeal and the appeal is upheld.

The judges could also send Pell’s appeal back to the Victoria Court of Appeals to be reheard by another three judges.

It is not known when the judges will deliver their rulings.

Pell is serving his sentence at the maximum-security Barwon Prison near Geelong, southwest of Melbourne. He hasn't traveled to Canberra for his appeal hearing.

One of Pell’s victims died of a heroin overdoses in 2014 without telling anyone of the abuse.

The survivor went to police after attending his friend’s funeral. Neither victim can be identified because the identities of sexual assault victims must be kept secret under state law.

Lisa Flynn, a lawyer for the dead choirboy's father who blames the abuse for his son drug attraction, said her client is “understandably quite anxious and unsettled” by the appeal.

"However he also remains very hopeful and also confident that the High Court will agree with the Court of Appeal majority and that the convictions against George Pell will be upheld,” she added.