Gardaí believe the car used by the killers of Detective Garda Adrian Donohoe was stolen in Clogherhead, Co Louth, and remained in the area days before the armed robbery.
The burnt-out Volkswagen Passat found in woods in south Armagh is being forensically examined by the PSNI, who are working closely with gardaí in the investigation.
Gardaí have issued an appeal for anyone who may have seen such a car either parked up or being driven around the area to contact the incident room in Dundalk.
It has also emerged that Garda Donohoe was not due to be on duty last Friday night, but was filling in for a colleague.
The killing and robbery took place at the Lordship Credit Union in Bellurgan, Jenkinstown in Co Louth on Friday night.
Detectives say the gunman did not hesitate before shooting the 41-year-old in the head and believe they are close to identifying the five members of the gang involved.
The investigation into the murder is focusing in on a cross-border gang.
Gardaí say they are grateful for the response they have received from the public to their appeal for information and they are checking every report.
They will make a national televised appeal this evening on Crimecall, which begins at 10.15pm on RTÉ One.
Detectives are examining CCTV footage taken from local businesses, petrol stations and the Lordship Credit Union.
Detective Garda Joe Ryan, who was held at gunpoint during the robbery, remains deeply traumatised.
Meanwhile, books of condolences remain open in several garda stations around the country and at the Mansion House in Dublin.
The remains of the father-of-two are reposing at his home this afternoon ahead of his State funeral tomorrow at St Joseph's Redemptorist Church in Dundalk.