GARDAI are satisfied that their murdered colleague Adrian Donohoe was lured into a trap and deliberately ambushed.
Senior officers say the armed robbers, who gunned him down in cold blood, were intent on murdering him as he approached them.
He was blasted in the head with a long-barrelled shotgun from almost point-blank range.
Last night the focus was on a cross-border gang, which is mainly based in south Armagh, as police on both sides worked closely together to track down the killers.
Officers are hopeful a detailed forensic examination of the dark-coloured Passat car, which was used in the getaway, will provide vital clues.
The car was found burnt out yesterday afternoon in a wooded area in south Armagh, not far from the Mountain Lodge Pentecostal Church at Darkley where three worshippers were murdered by the INLA and another seven injured in a massacre in November 1983.
The vehicle was destroyed but gardai and the PSNI believe a technical examination will yield some evidence.
Officers insisted it was still too early to determine whether the gunmen belonged to a criminal gang or a dissident terrorist group.
Gardai sifted through the available intelligence at a case conference in the investigation headquarters where Det Gda Donohoe and his wife, Caroline, both worked.
Det Gda Donohoe's patrol colleague was held at gunpoint after the murder while the raiders then stole €4,000.
The killers knew from surveillance they had carried out on the credit union at Lordship, outside Dundalk, that a garda escort was always provided for officials as they brought their cash on Friday nights after late opening to a night safe at a bank in the town.
The four raiders spoke with local accents and were armed with the shotgun, a handgun and a blunt weapon like a lump hammer.
Det Gda Donohoe (41) and his colleague, Detective Garda Joe Ryan, also from Dundalk station, were sitting in their unmarked patrol car and waiting to escort two credit union officials as they took out the cash.
One of the gunmen jumped out of the getaway car and made his way towards the officials, a man and a woman.
Det Gda Donohoe, who was the passenger in the patrol car, also got out to investigate but as he drew close to the gang, one of them produced the shotgun and fired at his head.
The father of two died instantly.
At the same time, the shotgun-wielding thug ran towards Det Gda Ryan and warned him that he would also be shot if he moved from his driver's seat or refused to give them the keys.
Other members of the gang then smashed the window of the officials' car with the hammer and snatched €4,000, leaving another haul of cash behind.
Officers said last night that the gang could have disabled the gardai by forcing them to hand over their weapons and shooting out the tyres of their car.
The intensity and cold-blooded nature of the violence at first indicated to investigators that the gang were likely to have been members of the new dissident terror alliance, who were already responsible for the murder of Northern Ireland prison officer David Black last November.
But over the weekend, the gardai were also involved with the PSNI in checking out the movements of a particularly violent gang, which has been operating on both sides of the Border and is believed to have been behind a €62,000 raid on the Lordship credit union in the autumn of 2011 when a shotgun was also used.
Police are also checking out the possibility of links between this gang and dissidents.
This week, gardai will trawl through footage taken from CCTV cameras in the area over the past month. A minute examination of the credit union car park and surrounding roadside is also being carried out to find potential fingerprint evidence, such as cigarette stubs or mineral bottles, that might have been left behind by gang members during surveillance of the premises on previous occasions.
"No stone is being left unturned," a senior investigator said last night. "This was butchery. Adrian didn't have a chance and had not drawn his official weapon.
"The gang knew the gardai would be there and they lured Adrian closer to them and shot him in cold blood."
Gardai from outside stations, including colleagues of Adrian's two brothers and brother-in-law, who are members of the force attached to stations in Swords, Navan and Limerick, contacted the investigation headquarters over the weekend and offered to use their rest days to help with inquiries into the murder.
Parish priest Fr Paidraig Murphy, who was at the scene minutes after the shooting, has spent the weekend trying to comfort widow Caroline and their two young children, Amy and Niall.
He said: "Like anybody, how do you cope in a situation like that? They are gradually coming to terms with it. They have had great support from colleagues and the local community, but there is still a human element – there is a wife, Caroline, who has lost her husband; and children who have lost their father."
In an online death notice, the dedicated policing family said Det Gda Donohoe was a beloved husband and adored father who would be forever missed.
It read: "Formerly County Cavan. Beloved husband of Caroline and adored dad of Amy and Niall. He will be forever missed by his beloved wife, daughter, son, parents Peggy and Hugh, parents-in-law Bridie and Stephen, sisters Mary and Anne, brothers Colm, Martin and Alan, brothers-in-law Derek, Kieran and John, sister-in-law Angela, nephews, nieces, relatives and friends."
A funeral service for Garda Donohoe will take place at St Joseph's Church, Dundalk, on Wednesday.