Lawyers for an Irishman described by the FBI as 'the largest facilitator of child porn in the world' have launched a "wide ranging" attack on the US justice system, according to lawyers for the Attorney General, in his appeal against an extradition order.

Eric Eoin Marques, who is alleged to be the owner and administrator of an anonymous hosting site known as Freedom Hosting, is wanted by the US authorities to face charges relating to conspiring to distribute and advertise child pornography and advertising and distributing child pornography.

The charges against Mr Marques relate to images on over a hundred "anonymous websites" described as being extremely violent, graphic and depicting the rape and torture of pre-pubescent children.

The 30-year-old with an address at Mountjoy Square in Dublin, has been in custody since his arrest in August 2013. 

His surrender was ordered by the High Court last December but this was stayed pending an appeal.

In the Court of Appeal today, counsel for Mr Marques, Micheál P O'Higgins SC, said it was not necessary to refer to the offences as alleged offences because his client had offered to plead guilty to them in Ireland.

The core point of the appeal was that Mr Marques' fair trial and due process rights would be violated if he was surrendered and there were substantial grounds for believing he was at "real risk" of being subjected to a "flagrant denial of justice".

The US sentencing system involved certain notions that were "really quite alien" not just in an Irish context but an international context also, Mr O'Higgins said.

It was a "startling state of affairs" that according to US case law, an American court is obliged to have regard to uncharged or acquitted conduct when sentencing a defendant, Mr O'Higgins submitted.

It could be done without the rules of evidence being applied, it could involve hearsay and matters from another trial entirely, which was "unheard of". It could be done in a "dangerous, uncontrolled way" where "poison could be poured into the case," Mr O'Higgins said.

An expert on US sentencing, whose affidavits were before the court, "says this is not just a possibility, it is routine," he added.

Mr O'Higgins said there was a danger Mr Marques would be sentenced for something he did not do.

Uncharged or acquitted conduct could be proved on the lesser balance of probability standard, which was "objectionable", he submitted, not just to Irish Constitutional law but also to international norms and the presumption of innocence.

Mr O'Higgins said he met the test set down in Supreme Court cases known as 'Rettinger' among others as well as the Strasbourg court in Abu Qatada - which laid down a stringent test "we say we come within".

The apprehended breaches of Mr Marques' Article 6 (of the European Convention of Human Rights) rights were a "nullification of the interests" Article 6 was designed to protect, counsel submitted.

Just because the US had not been called out on this issue, he said, did not invalidate the argument.

It was an Irish judge who "called out" the US on Article 3 solitary confinement issues in the extradition case known as 'Damache', Mr O'Higgins said.

Counsel for the Attorney General, Patrick McGrath SC, said the claims made by Mr Marques' lawyers were speculative and did not demonstrate real risk, as was necessary.

He said Mr Marques' lawyers had launched a "wide ranging, scatter-gun attack" on the US justice system "as far as sentencing goes".

The flagrant denial of justice test as asserted by Mr O'Higgins was a very stringent test, Mr McGrath said. It went beyond mere irregularities or lack of safe guards.

There was no authority or statement to say matters that went to sentencing had to be proved beyond a reasonable doubt.

Mr McGrath said it was incorrect to say sentencing judges in America were obliged to enhance sentences with uncharged or acquitted conduct, as Mr O'Higgins had submitted. Uncharged conduct may, he stressed, in certain circumstances be taken into account.

But there was no real risk that Mr Marques would be acquitted on one count, convicted on another and be punished on the count he was acquitted of. It simply did not arise, Mr McGrath said.

He added that relevant conduct could be considered. It was one among many factors to be considered by sentencing judges in America, he said.

Barrister Michael Lynn SC, for the Irish Human Rights and Equality Commission, whose role in the proceedings was impartial, told the court that the Abu Qattada case was a "seismic decision" that set the bar for surrender or deportation high.

Mr Lynn said any matter that could enhance a defendant's sentence should be proved beyond a reasonable doubt and a lower standard of proof would violate the European Convention on Human Rights.

Mr Lynn said a universal norm was something that was recognised by the international community as a requirement of law.

However, he added that the extradition of a person from Ireland to the US was not necessarily prevented because they would still have to show that a flagrant denial of justice would occur.

The hearing resumes before Mr Justice Michael Peart, Mr Justice George Birmingham and Mr Justice Garrett Sheehan tomorrow.