Aaron Brady has been found guilty of the capital murder of Detective Garda Adrian Donohoe during an armed robbery seven years ago.
It was the prosecution's case that Brady (29) fired the fatal shot during the raid at Lordship credit union in Dundalk, Co Louth, on January 25, 2013.
He denied this and claimed he was moving laundered diesel waste cubes at a yard in south Armagh at the time.
However, following a 28-week trial, the jury of seven women and five men returned guilty verdicts on counts of capital murder and robbery.
The longest murder trial in the history of the State began on January 27 and sat for 118 days, during which 139 witnesses were called to give evidence, including the accused.
The defence had made several applications to discharge the jury, citing the delay over the Covid-19 pandemic and the interruption of a key witness' testimony, but these were refused by trial judge Mr Justice Michael White.
Brady, of New Road, Cross- maglen, Co Armagh, now faces the mandatory 40-year prison sentence after being convicted of capital murder.
Det Gda Donohoe (41), a married father-of-two, was on an armed cash escort when the convoy was ambushed by a five-man gang as they prepared to leave the credit union.
The detective had stepped out of his unmarked Toyota Avensis after the car park exit was blocked by a Volkswagen Passat when, without warning, he was shot in the head at point-blank range.
He was the 87th member of An Garda Síochána to die in the line of duty.
The raid was carried out in 58 seconds and netted the gang €7,000, while €27,000 was left behind.
The prosecution said the robbery must have been carried out by a local gang - they had border accents and know- ledge of the rural getaway roads used and were motivated by money.
The prosecution had relied on what they said was "overwhelmingly" circumstantial evidence, tied together with the admissions of the accused and wrapped in a litany of lies, to prove beyond reasonable doubt that Brady shot Det Gda Donohoe.
The Passat used in the robbery had been stolen from Clogherhead during a 'creeper' burglary three nights before the murder.
There was expert evidence given that a distinctive BMW 5 Series with a metallic wrapped roof captured on CCTV close to the burglary that night was very similar to a BMW belonging to Brady's best friend, Suspect A.
The prosecution said there was a silent period on both of the men's phones at this time, indicating that they were in each other's company when the getaway car was stolen.
Mobile phones belonging to the accused and three other suspects were also inactive during the same period an hour before and after the murder.
Prosecutor Lorcan Staines SC described this as an "extraordinary unusual and unlucky coincidence".
Brady was described as a "skilled and practised liar".
He admitted he lied when giving an account of his movements to Inspector John Moroney the day after the murder, and again 10 days later when he made a voluntary statement to Det Gda Jim McGovern and Det Insp Mark Phillips.
Brady had claimed he lied because he was trying to hide the fact he was moving laundered diesel waste, but the prosecution said it was to hide his involvement in the murder.
They said these lies continued when Brady got into the witness box of the Central Criminal Court.
Over the course of five days, he denied any involvement in the murder and described key prosecution witness Daniel Cahill as a "psychopath" and a "pathological liar".
Under cross-examination by lead prosecution counsel Brendan Grehan SC, Brady claimed he had been a victim of a campaign by An Garda Síochána and the media.
The jury heard that within weeks of the robbery, Brady and three other suspects left Ireland and travelled to "far-flung corners of the world".
The accused settled in the Woodlawn area of the Bronx, New York, where he "wore the shooting of Det Gda Adrian Donohoe like a badge of honour".
There was damning evidence from two witnesses living in the US, who told the court they heard Brady make admissions.
Molly Staunton, an American citizen, said she was in Brady's apartment when he was "ranting" about having "murdered a cop" in Ireland.
While appearing via video link, her evidence was interrupted by a friend, who told her to "put a stop to it" and "no more testimony" before the live feed cut off.
Mr Justice Michael White gave the jury a warning about her evidence.
Daniel Cahill, a barman who worked in the Bronx, told the trial of three interactions he had with Brady, during which the accused said he had shot a guard in Ireland.
One incident happened after the accused was punched in a bar fight, another while he was drinking on his own in a pub saying he had nightmares about the shooting and a third was in an apartment where Brady bragged about the murder.
Mr Cahill told the court these admissions happened between 2015 and 2016 in the Bronx and that on each occasion Brady said he had shot a garda.
During the trial, the court heard Mr Cahill was out of residency status in the US and was waiting to apply for a green card, having married an American citizen.
Homeland Security agent Mary Ann Wade, who detained the witness last year before he gave his statement, gave evidence that Mr Cahill was not made any offers for his co- operation.
A letter of scope provided to her by her employer limited the evidence she could give in a foreign court.
The prosecution contended that, if all of the evidence against Brady was "a lie, bad luck and strange circumstances", it would be "some string of unfortunate events" for him.
It was the defence's case that the accused was at a diesel laundering yard 21km away from Lordship credit union at the time of the robbery.
In the end, the jury took just over 20 hours to find Brady guilty of robbery and of the capital murder of Det Gda Donohoe.