Evidence from 'master' and 'slave' handsets helped to place killer and victim together
The High Court has ruled the Irish law under which gardaí gathered mobile phone evidence against Graham Dwyer contravenes EU law and the European Convention on Human Rights. Does this mean his conviction for the murder of Elaine O'Hara has been overturned?
No. Dwyer's conviction was not being considered by the High Court. It was examining the compatibility of the 2011 Communications Act with EU laws. Dwyer now plans to use the ruling to support an appeal against his conviction in the Court of Appeal.
Will the High Court ruling have a bearing on his appeal?
It could. On the face of things, it certainly boosts one of his grounds of appeal, which is that the trial judge made an error when he allowed certain mobile phone data to be entered in evidence.
However, it is possible the appeals court may still find that the evidence was admissible.
When is his appeal being heard?
No date has been set for it yet. There is speculation it could be heard some time next year.
However, should the Garda Commissioner and the State appeal yesterday's High Court ruling, it would set a potential appeal date back considerably.
Was the High Court ruling expected?
It was not a total surprise. The 2011 Act gave effect to the EU's 2006 Data Retention Directive. But this directive was declared invalid by the European Court of Justice in 2014.
What is wrong with the Irish law?
Mr Justice Tony O'Connor found the act was in breach of human rights law because there was no prior review by a court or an independent authority for access to telephony data.
What has the reaction been to the ruling?
Justice Minister Charlie Flanagan said it was clear that the current legal framework allowing for access to communications meta-data to combat criminals and terrorists needs to be modernised. The minister said a new Data Retention Bill was at an advanced stage of being drafted and was on the Government's priority legislation list.
The Irish Council for Civil Liberties called on the Government to move quickly to introduce comprehensive data-retention legislation that fully respects individual rights.
Why was mobile phone data so important in this case?
This evidence was able to place Dwyer and his victim together. Detectives were also able to "resurrect" text messages from phones and computers to reconstruct conversations between Dwyer and Ms O'Hara.
Using the 2011 Act, gardaí obtained data associated with Dwyer's work mobile phone and other handsets.
Using cell-site analysis, they were able to pinpoint roughly where Dwyer was at certain points in time based on the movements of his phone.
This helped investigators establish his routine in the months prior to Ms O'Hara's disappearance.
Cell-site analysis was also able to link the movements of Dwyer's work phone to those of a Nokia mobile phone found in the Vartry Reservoir in Co Wicklow in September 2013.
When Dwyer went somewhere, he tended to bring both phones with him.
This second handset, known as the "master" phone, was used by Dwyer to communicate with Ms O'Hara.
She used another Nokia handset, known as the "slave" phone, which gardaí recovered during the investigation. Both the "master" and "slave" phones were detected in Shankill, Co Dublin, on the night Ms O'Hara disappeared.