Barry Doyle, aged 29, of Portland Row, Dublin, was jailed for life five years ago for the murder of Mr Geoghegan in Limerick on November 9, 2008.
Doyle had been brought from Dublin by a Limerick criminal gang to kill a rival criminal but, instead, shot dead Mr Geoghegan in a case of mistaken identity.
His appeal raised issues concerning the right of access to a solicitor.
The Chief Justice, Susan Denham, was among the six judges who dismissed Doyle’s appeal on different bases.
All seven judges agreed there is a constitutional right of reasonable access to a solicitor, but a majority agreed there is no constitutional right to have a solicitor present during questioning.
Mr Justice Peter Charleton, whose judgment was endorsed by a majority, held the Constitution should be interpreted as requiring and guaranteeing access to a lawyer, but does not require a lawyer be present during interviewing.
The disputed interview with Mr Doyle, his 15th, in which he told gardaí: ‘Yeah, I shot him’, was video- recorded.
Doyle later refused to name anyone else involved but removed a set of a rosary beads from around his neck, a memento of his own dead brother, for gardaí to give to the Geoghegan family as a mark of his remorse, the judge noted.
A range of safeguards and protections for detained persons now available, including a right of access to legal advice prior to questioning, were not available in the past, the judge said.
It is not a necessary part of the right to a trial in due course of law under Article 38.1 of the Constitution that a lawyer should be present for the interviewing of a suspect in Garda custody, he held.
Mr Justice Donal O’Donnell, Ms Justice Mary Laffoy, and the Chief Justice, agreed on that point, but Ms Justice Iseult O’Malley reserved her position on the constitutional right to have a solicitor present at interview to a future more appropriate case, saying that issue did not truly arise on the facts of this case.
She agreed with Mr Justice John MacMenamim that Doyle had failed to show any causative link between his admissions and the alleged breach of a putative constitutional right to have a solicitor present during an interview.
Mr Justice MacMenamin held the Constitution, in principle, requires in future a lawyer be present for the interrogation, but also found Doyle’s admission of killing Mr Geoghegan would not be excluded.
In his dissenting judgment, Mr Justice William McKechnie said it was of “fundamental importance”, and necessary to fully protect and vindicate the rights of a suspect, to have a solicitor present during garda interrogation.
Doyle alleged gardaí induced an admission of the murder from him, but the Court of Appeal found that Doyle knew what he was doing when he made the admission.
That court noted that it was Doyle’s solicitor who approached gardaí with an offer that Doyle would say he killed Shane Geoghegan if gardaí agreed to release his girlfriend, the mother of his then one-year-old daughter, from custody.