The Supreme Court is due to begin hearing the State’s appeal against the successful action taken by Graham Dwyer over data retention legislation.

The convicted murderer won an important ruling in the High Court last year on the retention and access of mobile phone data.

All of the evidence presented during Graham Dwyer’s trial four years ago was circumstantial and one of the main planks of the case against him involved the use of mobile phone data, which allowed the prosecution to show where he was at certain relevant times.

The lengthy trial ended with the jury finding the Cork-born architect guilty of murdering Elaine O’Hara in the Dublin Mountains in August 2012.

The law that allowed his phone data to be retained and later accessed by investigating Gardaí stemmed from a European directive that has since been declared invalid.

Last year, the High Court found the legislation to be in breach of EU law because it was too “general and indiscriminate”.

Given the significance of the ruling, the Supreme Court allowed this appeal to leapfrog others and it’s due to begin hearing submissions this morning.

Dwyer has yet to appeal his murder conviction, but is likely to do so once the court rules on the State’s attempt to overturn last year’s judgement.

Reporting from Frank Greaney