Cardinal George Pell’s lawyer, Bret Walker SC, has told three judges presiding over his client’s appeal that the timing of Pell’s offending was a “critical matter” in deciding whether his conviction should be overturned.

Walker is appealing Pell’s conviction on three grounds, the key one being that the jury came to an unreasonable verdict based on the evidence before them during the trial.

Jurors heard that the first offences, which involved Pell sexually assaulting two 13-year-old choir boys after Sunday solemn mass at St Patrick’s Cathedral in Melbourne, most likely occurred on either 15 or 22 December 1996. Pell orally raped one of the boys during this incident and indecently assaulted both of them.

The jurors heard Pell offended again about one month later when he grabbed the complainant’s genitals, once again after Sunday mass.

But the Crown’s written case to the appellate judges states that 3 November 1996 may have also been a possible date when the first offences occurred, as it had not been established during the trial that Pell was not present at mass on that date.

The introduction of 3 November as another possible date was “in itself disturbing ... and should disturb this court”, Walker told Victorian supreme court chief justice Anne Ferguson, court of appeal president justice Chris Maxwell and justice Mark Weinberg.

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It revealed the Crown’s own “doubts involving the theory that this supposed first event or incident indeed took place on the 15 or 22 of December”, Walker said. “And if it didn’t take place on one of those two dates then the Crown case fails.”

This was because the complainant said the second incident – Pell grabbing his genitals – occurred about one month later.

“There’s more than a month … well and truly … between 3 November and either 15 or 22 of December,” Walker said. It was in reviewing this timing that the judges should find a “lack of realistic probability of this offending taking place”, he said.

Pell, 77, was convicted in December on four charges of an indecent act on a child under the age of 16, and one charge of sexual penetration of a child under 16.

In his opening remarks on Wednesday morning, Walker also argued there was a “formidable list” of factors and events that needed to line up for the offending to be possible and the jury would have had to believe every one of those factors had occurred. This included believing that Pell was alone for about six minutes with the boys in the priests’ sacristy completely undisturbed, and possibly with the door open, after mass, he said.

It was “literally impossible” for the boys to have been abused, he said.

Maxwell put it to Walker that someone who was in New Zealand at the time they were alleged to have offended in Australia would be an example of an impossibility that they had offended. He questioned whether it was accurate for defence to argue Pell’s offending was impossible, given there was varying testimony from witnesses in the case in regards to choirboy access to the sacristy, Pell’s routine after mass, and other matters.

“The argument for impossibility… logically loses its force as uncertainty grows,” Maxwell said. “Your point is… and you’ve confirmed it several times… the evidence established such high improbability verging on impossibility there must have been a doubt. I’m just raising the notion… the greater uncertainty, the less forceful the argument for impossibility becomes. That must be true mustn’t it?.”

Walker responded: “No”.

During their closing arguments in the trial, prosecutors pointed to numerous pieces of evidence that demonstrated why the offending was possible. Jurors were also told it was not enough to just believe the complainant, or to think Pell was lying. They had to be convinced beyond reasonable doubt.

If Walker fails to convince the court that Pell’s conviction should be overturned on grounds of unreasonableness, he will fall back on two other grounds of appeal. One being that Pell was not arraigned in the presence of the jury panel; and the other being that Pell’s defence team should have been allowed to show a video animation of its argument during the closing address. The court accepting the appeal on these grounds would most likely result in a retrial rather than his conviction being overturned.

Family members and supporters of Pell and the complainant sat in the front row of the court, which was at capacity. An overflow room was opened with a video link to the courtroom to accommodate those who could not get a seat. Supporters of the complainant and the second choirboy, who died in 2014, were also in the court.

Pell attended in person, brought from the Melbourne Assessment Prison in West Melbourne where he has been held since February when he was sentenced to six years in prison. He dressed in all black and wore his clerical collar, limping slightly as he walked into the court. He occasionally took notes on a yellow notepad and watched Walker and the judges intently. Police officers sat behind him.

The prosecution’s response to the appeal is being led by senior crown prosecutor Christopher Boyce and assisted by prosecutors Mark Gibson, who led the trial, and prosecutor Angela Ellis. Walker is being assisted by defence barrister Ruth Shann.

When prosecutors put their case to the court, they will argue, according to their written submission, that the complainant’s evidence was “not only plausible, it was credible, clear and entirely believable as is reflected in the jury’s verdict”.

“The ability of the complainant to so accurately describe the layout and wood panelling of the priests’ sacristy (including the alcove) – an area in which he could not recall having ever seen either before or after this event – was a significant aspect of the Crown case,” the submission states. “It bespoke both truthfulness and reliability. Any inconsistencies in the complainant’s evidence were of little moment and could not have been said to have impacted on his credibility in any material way.”

Walker told the court doubt should have also been raised among jurors from evidence that Pell’s second victim denied he had been abused before he died. When the court adjourned for lunch, lawyer Lisa Flynn, representing the father of the dead victim, said that argument should hold “little persuasion”.

“Having represented thousands of sex abuse victims, I can tell you that it is not uncommon for victims to wait decades before opening up about what happened to them, a lot even take it to their grave,” she said.

“It is not unusual to deny abuse, particularly to parents. Many survivors find it impossible to tell their parents, their beloved mum or dad.”

Walker was questioned throughout the day by the judges. Maxwell put it to him that “you wouldn’t expect perfect recall” from a child sexual abuse victim. He also told Walker: “We have to be satisfied don’t we that the jury must have had a doubt, not might have.”

Maxwell said on his reading of the trial evidence, a significant component of the defence’s case was that the complainant was a liar. The jurors would have considered the plausibility of this argument in making their verdict, Maxwell said.

Walker responded that just because the jurors rejected this argument, it didn’t mean they shouldn’t still carry reasonable doubt.

Before Walker finished on Thursday, he was asked by the judges to address the issue of the robes. In the trial and in the appeal, Pell’s lawyers argued that it was physically impossible for Pell to manoeuvre his robes to the side in order to expose his penis as the complainant said.

Ferguson put it to Walker that the chasuble, which is the outer layer, was like a cape and could be moved to the side. Walker said that would still leave the alb underneath, which could not be manoeuvred to the side.

Prosecutors will deliver their response on Thursday and the appeal is expected to close that afternoon. While the judges may deliver their decision at the close of the appeal, it is more likely they will do so at a later date.

The hearing continues.