The unanimous decision of the High Court of Australia in Pell v The Queen raises an important question. Can a high-profile ­defendant receive a fair trial in the age of rampant social media?

Cardinal George Pell was found guilty of historical child ­sexual abuse offences in a second trial following a hung jury at the first trial.

Peter Kidd, the chief judge of the County Court of Victoria, properly instructed jurors that they should delete all thoughts they might have had about the defendant when they were empaneled. But is this possible, especially in view of what we know about ­unconscious bias?

The fact is that no defendant in modern Australia has been subjected to such a media pile-on as Pell. The attack included journalists, commentators and entertainers who were, in fact, Pell antagonists. The list includes (in alphabetical order) Richard Ackland, Paul Bongiorno, Barrie Cassidy, Richard Carleton, Peter FitzSimons, Ray Hadley, Derryn Hinch, David Marr, Louise Milligan, Tim Minchin, Lucie Morris-Marr, Jack Waterford and more besides.

The ABC led the campaign in programs such as 7.30, Four Corners, Lateline (as it then was), Q&A, News Breakfast and Radio National Breakfast.

There was also Nine’s 60 Minutes, Ten’s The Project, and Nine Entertainment newspapers The Age, and The Sydney Morning Herald, plus Guardian Australia, The New Daily and The Saturday Paper. Some of the papers occasionally contained articles by disinterested commentators.

There have been other media campaigns in contentious criminal cases, most notably in the case of Colin Campbell Ross, who was hanged in Melbourne Gaol in 1922 after he was found guilty of the rape and murder of a 12-year-old girl. He was pardoned posthumously in 2008.

Then there is the trial and conviction in 1982 of Lindy Chamberlain for the murder of her baby daughter. Her conviction was quashed in 1988.

And then there’s the Pell case. The crusade against Australia’s most senior Catholic was accentuated by the fact his trial took place when media reportage and commentary had been amplified by social media. Jurors are no longer locked up during trials and they are allowed to retain their phones. No court can guarantee jurors will not follow a case online.

In all mainland states except Victoria, defendants have a right to seek trial by judge alone. Victoria is now considering such a move. But it’s a bit late in the Pell case.

In view of this, there is a responsibility on the media to behave professionally while providing information to the public.

This did not happen with respect to Pell. In fact, Melbourne University Press brought forward the planned publication of ABC journalist Milligan’s book Cardinal: The Rise and Fall of ­George Pell to before his trial first began in June 2017.

Milligan led the “Get Pell” cause when, in July 2016, 7.30 devoted an entire program to the issue. Today, the ABC is standing by Milligan and Milligan is standing by her book.

This despite the fact it essentially accuses Pell of two sets of offences that have never been established.

The first, concerning crimes that allegedly took place in Melbourne’s St Patrick’s Cathedral in 1996, was the subject of the High Court’s decision to free Pell on Tuesday. The court found that “there is a significant possibility … that an innocent person has been convicted”.

Milligan’s second essential claim, that Pell assaulted two boys in Ballarat’s Eureka Swimming Pool in the early 1970s, was withdrawn by the Victorian Director of Public Prosecutions. Yet Milligan’s book is essentially a case for the prosecution which, in the final analysis, failed.

The lesson seems to be: once a Pell antagonist, always a Pell ­antagonist. Some ABC operatives who attacked Pell before and after his trial appear determined not to change their minds after the High Court decision. On Tuesday, ABC One Plus One presenter Cassidy tweeted about Pell that “the High Court has found there was not enough evidence to convict; it did not find him innocent”.

In fact, ­appellant courts do not find individuals innocent. An acquittal is as far as the High Court goes in such cases.

RN Breakfast presenter Fran Kelly got into a similar state of confusion on Thursday when interviewing University of South Australia law professor Rick Sarre and Victorian barrister Matt Collins QC.

Kelly started the interview by declaring that “our justice system is based on the primacy and importance of verdict by jury”.

For starters, outside of Victoria and Tasmania, this is not the case. Moreover, as Collins pointed out, “it is not unheard of” for the High Court to overturn a jury verdict.

In fact, in Pell v The Queen the seven judges referred to such High Court precedents as M v The Queen (1994).

Kelly also was surprised that the High Court had overturned a majority decision in the Victorian Court of Appeal.

Sarre had to tell her that it is “not unusual” at all. Sarre also commented that “there are going to be some times where the jury just may not be able to set aside every other prejudice or media report and just can’t have a fresh look at something”.

He added that “there are going to be some times when jurors might just stray away from the truth”. That’s a particular problem when a media operation against a defendant is in place.

Then there is the wider problem of media-inspired collective guilt. In his foreword to Cardinal, author Tom Keneally focused on Pell’s (alleged) responsibility for “the victims of churchmen”.

Now, none of Pell’s supporters deny the crimes of some priests and brothers, especially since Pell was one of the first church leaders to take action against clerical child sexual abuse.

The point is that Pell was not charged with the crimes of churchmen. He was charged with respect to two specific matters — and was acquitted by the highest court in the land.

The reality of the media pile-on and the concept of collective guilt threatens the criminal justice system, especially in Victoria where there is no right to trial by judge alone.