A man accused of supplying the car used in the murder of David Black was an integral part of the plot.
Prosecutors claimed CCTV evidence supports their case that Damien McLaughlin transported a Toyota Camry vehicle across the border on the eve of the dissident republican attack on the prison officer.
Mr Black, 52, was shot dead on the M1 Motorway near Lurgan as he drove to work at HMP Maghaberry on 1 November 2012.
Mr McLaughlin, 36, of Kilmascally Road, Dungannon, Co Tyrone, denies a charge of preparation of a terrorist act.
He was refused compassionate bail to attend his child's christening service tomorrow.
The High Court in Belfast heard how the car used by the killers was bought in Dublin for €600 through a Gumtree ad last October.
False details were supplied by the purchaser, who is not alleged to be Mr McLaughlin, according to the prosecution.
The car was said to have been moved to Carrigallen, Co Leitrim where it remained for nearly three weeks.
The prosecution also claimed CCTV footage shows Mr McLaughlin in the village on 31 October. It was alleged that he obtained a car battery used to start the vehicle.
Later that evening, the car was known to have crossed the border into Northern Ireland, leaving the M1 near Lurgan, the court heard.
Mr Black was shot dead the next morning after leaving his home to head for the high-security prison.
The Toyota Camry was later found burnt-out.
Opposing Mr McLaughlin's attempt to get temporary release, the prosecution lawyer outlined police fears that he may flee.
The barrister also stressed that Mr McLaughlin is not suspected of just having a periphery involvement.
Defence counsel Mark Mulholland QC argued that his client must be presumed innocent.
He claimed the case against Mr McLaughlin was "sparse", limited only to him allegedly being in the car the night before the murder.
He disclosed that a priest was prepared to chaperone the accused at the christening in Ardboe.
Relatives were also prepared to lodge £13,000 in cash sureties and property deeds to secure bail.
But refusing the application, Mr Justice Treacy pointed out that Mr McLaughlin's wife would have been heavily pregnant at the time he was alleged to have been involved in the terrorist plot.
The judge added: "It is untenable to expect or reasonably contemplate in those circumstances this court or any court would release this applicant on bail given the grave risks that would give rise to."