There are "enormous amounts" at stake in convicted murderer Graham Dwyer's case over the retention and access of his mobile phone data, the Supreme Court has been told.
The State is appealing the High Court's decision last year, which found part of the legislation allowing mobile phone metadata to be retained and accessed in the investigation of serious crimes breached EU law and the European Convention on Human Rights.
Such data played a significant role in the successful prosecution of Dwyer in 2015 for the murder of Elaine O'Hara in 2012.
The prosecution was able to show where Dwyer's phone was at certain times and what numbers it was in contact with.
Gardaí were able to get this information under Irish legislation brought in following a European directive, which was later declared invalid.
The High Court found the legislation allowing such data to be retained was general and indiscriminate and breached EU law.
It said the Court of Justice of the EU had ruled that even the objective of fighting serious crime, could not justify such an indiscriminate regime of retaining data.
The High Court ruled the system of accessing the data breached the European Convention on Human Rights because there was no prior review by an independent authority before it could be accessed.
The State appealed and the appeal went directly to the Supreme Court because of the importance of the legal issues involved.
This morning, Senior Counsel Paul Gallagher, for the State, said the case raised fundamental questions about telecommunications metadata.
He said the Supreme Court dealt with immensely important cases, but there were "enormous amounts" at stake in this one, not only in relation to Dwyer's conviction, but in relation to the powers of the State in retaining metadata and accessing it in the context of the fight against serious crime.
Mr Gallagher said we lived in a digital society and mobile phones played a critical part in communications and had fundamental implications in preventing, investigating and prosecuting crime.
If the High Court judgment were to stand, he said, it would mean there was a virtual space in which criminality existed and could not be accessed by State authorities.
Mr Gallagher said the State was contending there were errors in the existing case law from the Court of Justice of the EU.
He said the State's case was that the principles of those cases, properly understood, did not prevent the retention and access of such data.
But he said if the State was wrong, it was something that the CJEU needed to clarify or revisit.
Mr Gallagher said the absence of a system allowing the general retention of data, of the type Ireland operated, was a very significant impediment to protecting citizens from crime and to prosecuting crime.
He said the access to mobile phone metadata played a significant role in Dwyer's prosecution, but there was other compelling independent evidence.
Dwyer's appeal against his conviction is on hold pending the outcome of these proceedings.
