Now charges have been laid against Cardinal Archbishop George Pell, we are in an unprecedented historical position.

The as-yet undisclosed charges will be under Victorian state law, and subject to the rules of evidence, meaning Victoria Police have decided some of the existing allegations or testimony may withstand cross-examination in a court of law. That is a high bar.

The Cardinal strenuously denies the allegations made against him and has said in a statement he will return to Australia as soon as possible, pending the approval of his doctors.

Health withstanding, it would be legally possible for him to remain in the Vatican, unless Pope Francis ordered him to return to Australia.

Under the Catholic Church's international code of canon law, the Pope is the "supreme legislator", and is in charge of the Church, legally and spiritually, throughout the world.

But there is no modern precedent for a pope ordering a cardinal to return and answer to a foreign legal jurisdiction.

Pell still a possible future pope

The police have decided to prosecute a potential world leader. The Ballarat-born 75-year-old is still a possible pope in waiting. All it takes is for Pope Francis to die suddenly, and one of the 120-odd Cardinals will be the next pope. It could be Cardinal Pell.

Cardinal Pell is the head of the Vatican secretariat for the economy. Effectively he is the third in charge of the 1.2 billion-member Catholic Church.

The Cardinal has diplomatic immunity, and Australia has no extradition treaty with the Vatican. We have one with Italy, but not the Vatican itself.

In the modern era, laying serious or criminal charges against a Cardinal has not been done in a free and democratic nation where immunity could apply.

There is the ongoing matter of Archbishop Wilson of Adelaide, who was charged for failing to report a serious offence under the NSW Crimes Act, but Archbishop Wilson is not a Cardinal.

Supporters of Cardinal Pell may compare the case to the scandalous 1948 show trial of Hungarian Cardinal József Mindszenty, who was tortured and then was found guilty of treason.

But there are two other shocking prior cases involving Americans that are really worth recalling. They concern Cardinal Archbishop Bernard Law of Boston, and Vatican banker Archbishop Paul Marcinkus.

Cardinal Law was the Archbishop of Boston. The sexual assault of children by clergy was rife in Boston under his watch.

If you've seen the movie Spotlight, you have some sense of the depraved situation, and the enormity of the damage done to children and families.

Vatican gave diplomatic immunity to Cardinal Law

Cardinal Law was named a defendant in a number of serious and public cases involving paedophile priests.

The Boston Globe blew the whistle on extensive cover-ups in the archdiocese in 2002 and Cardinal Law resigned as Archbishop in December that year. The Massachusetts state attorney-general launched an investigation into sex abuse and the Church.

When the report was published in 2003, it said that under Cardinal Law's watch, the archdiocese of Boston had "made choices that allowed the abuse to continue".

But it went on to say the cardinal had not broken any laws, since Massachusetts laws requiring priests to report abuse had not been introduced until 2002.

But after his resignation in disgrace, Cardinal Law went to the Vatican where he was given diplomatic immunity, a flat and a job by Pope John Paul II.

The pope then gave him the honoured position of Archpriest of St Mary Major's basilica, one of the seven great churches of Rome.

He has never been charged concerning the crimes committed by priests under his watch in Boston. He is now retired in the Vatican.

Subjected to moral disapproval, critical press but no charges

Archbishop Paul Marcinkus was the head of the Vatican Bank from 1971 to 1989. He presided over the Vatican Bank scandal, which involved, at various stages, suicide or murder and complex links to organised crime.

On April 24, 1973, Marcinkus faced questioning at the Vatican by a US federal prosecutor. The head of the organised crime and racketeering section of the US department of justice also questioned the Archbishop.

George Pell's early career as a priest was in Victoria's Ballarat area. ( Supplied )

It concerned his role in the delivery of US$14.5 million worth of counterfeit bonds to the Vatican in July 1971. There was much more money involved.

Marcinkus was never charged. After all the financial scandal and crimes had been exposed, the Marcinkus case was deemed unable to be pursued under US law.

He eventually returned home to the US, where he died in 2006.

In the cases of Cardinal Law and Archbishop Marcinkus, no charges were laid. The cardinal and the archbishop were subject to moral disapproval and sharply critical press, but no charges under law.

Lack of sufficient evidence, or the absence of mandatory reporting laws, meant they were not legally accountable either under US federal law or Massachusetts state law. And here is where legal jurisdictions really matter.

The matters of Cardinal Law and Archbishop Marcinkus could once have been seen as parallel to the case of the Cardinal; much said in the press, much formal questioning, but no charges.

But now the Cardinal is required to appear at the Melbourne Magistrates' Court on July 18.

We are in completely new territory.

Editor's note: On Tuesday April 7, 2020, the High Court in a unanimous decision upheld Cardinal Pell's appeal and quashed his convictions on all five charges.