The two-car convoy pulled into the car park of Lordship Credit Union on the Cooley Peninsula shortly before 9.30pm on Friday, January 25, last year.
The first car was driven by an official carrying cash from another credit union branch for lodgment in the bank night-safe in Dundalk.
The second was an unmarked squad car with two detectives, Adrian Donohoe and Joe Ryan, who were providing an armed escort.
They drove into the cut stonewalled car park and turned around at the front of the building to face back out towards the exit.
Everything seemed routine as they met with a female official from Lordship who was also taking cash to the same night safe in a third car.
As the small convoy was about to leave, the exit was suddenly blocked by a stolen VW Passat car.
As Adrian Donohoe, who was in the passenger seat, got out to investigate, four figures jumped across the boundary wall and charged in his direction.
The raiders ran towards the cars, in the direction of the driver's side. They split up into two pairs – one went towards the Lordship official's car and the other towards the squad car.
As he reached the island, one of the men was recorded holding a full-length shotgun in his hands and fired in the direction of Det Gda Donohoe.
The "gentle giant", who was hit at close range in the back and side of the head, collapsed instantly.
He never stood a chance.
Even after Det Gda Donohoe hit the ground the gang continued with their robbery. There was no sign of panic, suggesting that they had planned for potential fatalities.
Two of the raiders smashed in the window of the Lordship official's car and grabbed the bag of cash and the woman's handbag.
At the same time, Detective Garda Joe Ryan was pulled from the car and forced to lie on the ground. One of the killers threatened him: "We'll put one in your head."
The gang piled into the stolen car and drove off at speed towards the 'bandit country' of south Armagh.
The crime that shocked and stunned the nation was over in less than two minutes and recorded in grainy horror on the credit union's CCTV cameras.
It didn't take gardai long to identify the suspects for the cold-blooded murder of the 41-year-old devoted husband and father.
Gardai believe at least five well-known criminals from south Armagh were involved and they are satisfied that they also know who fired the fatal shot.
They haven't yet ruled out the possibility that a sixth accomplice, a woman, drove the getaway car which was found burned out two days later in a wood.
The investigation launched by the tragic garda's colleagues is one of the largest seen in recent years in Ireland and now has an international element.
Members of the gang spent time in the US while one went to work for a year in Australia in the months following the murder.
Gardai have received assistance from the FBI, Europol and Interpol as well as law enforcement agencies in the UK, Holland and Australia.
Detectives have travelled to the US and Australia to interview the suspects who have all refused to make statements.
Three gang members are due to return to south Armagh from Australia and the US when their visas run out in the coming weeks.
Meanwhile, the investigation, which the commissioner has conceded has been slow and at times painful, is making progress.
A team of detectives are still painstakingly sifting through a mountain of CCTV footage – 40 years' worth in actual time.
Over recent months they have unearthed material which is described as important to the overall inquiry. There is also a crucial DNA sample taken from a mallet hammer the gang left at the scene.
Senior sources say that slowly but surely the evidential case is building that will eventually result in charges.
But gardai are also faced with another enemy in their quest for the truth – silence.
In the year since the murder, the perpetrators have been protected behind the same wall of silence constructed by the IRA during the 30 years of the Troubles.
Officers are aware that the mother of two gang members and the father of another, have been actively involved in making sure that no one talks.
The thugs have been briefed by their elders, who know more about such things, on how to thwart murder investigations.
But despite the barriers to success so far, the gardai are determined that no matter how long it takes they will solve this murder.
By Paul Williams