Gardai said they are confident of charging Detective Garda Adrian Donohoe's killers as it emerged that officers have made "significant progress" in linking the stolen car that was used in the murder to the gang.
The development comes after a special Mass was held in Dundalk, Co Louth, on Tuesday night to mark what would have been the father of two's 42nd birthday.
There will also be a Mass later this month to mark the first anniversary of his death.
It has also emerged that Gda Donohoe's wife Caroline, who is also a garda, has not returned to work since the murder that shocked the country.
Gda Donohoe was shot dead during a botched robbery by a local gang at Lordship credit union at 9.30pm last January 25.
A source told the Herald: "Some people may be suggesting that this investigation is going nowhere, but that is not the truth at all.
"Very good CCTV and mobile phone evidence has been gathered, and one line of the investigation that is being pursued fairly vigorously at the moment is linking the gang with the stolen car used in the murder."
The graphite blue Volkswagen Passat was stolen in Clogherhead, Co Louth, between 11.30pm on January 22 and 4.30pm on January 23.
It was found burnt-out at Cumsons Road, Newtownhamilton, Co Armagh, about an hour after Gda Donohue was murdered.
Two men have already been questioned about the theft of the car, but no charges have been brought.
The Herald previously revealed that the holiday visas of two men who flew to New York after their suspected involvement in the murder are due to expire shortly.
The suspects, including the criminal who is believed to have fired the shotgun, cannot be extradited unless the Director of Public Prosecutions rules that they should face criminal charges.
They can, however, be deported if they overstay their visas.
Gda Donohoe was blasted in the head when he confronted a gang on rural roads near his home on the Cooley peninsula.
The five-man gang, which includes two brothers, are all from south Armagh.
It is understood that the PSNI has quizzed a number of the gang members believed to have been involved in the murder, including a young woman who provided an alibi for her boyfriend who is suspected of being at the scene on the night.
This suspect has not fled to the US.