Police on both sides of the Irish border believe a North Louth-South Armagh based gang of thieves are responsible for the murder of detective Adrian Donohoe on the Cooley Peninsula.
A car understood to have been used as the getaway vehicle has been found, burnt-out, in Keady.
The car was discovered 25 miles from the scene of the crime in Bellurgan.
Police Service of Northern Ireland officials are now working closely with their southern counterparts to catch Donohoe’s killers.
The 41-year-old father of two was shot dead as he arrived at a credit union in County Louth last Friday night to provide an armed escort with a colleague.
The gang escaped with just over $5,000 in cash which was to have been lodged in a bank in nearby Dundalk.
Detectives working on a case have described it as ‘cold blooded murder’ according to a report in the Irish Times.
The Republic’s Minister for Justice Alan Shatter and police commissioner Martin Callinan have publicly condemned the killing.
Minister Shatter vowed that no resources would be spared in the search for the murderers.
Officers believe the gang had a very good knowledge of the road network in the area and were well aware of the times for the regular Friday night movement of cash from the credit union into Dundalk.
The report adds that a gang of criminals from north Louth-south Armagh are the chief suspects.
They had previously raided the local post office in 2011 when they escaped with almost $100,000 as armed police were about to arrive to escort the cash into a bank night safe in Dundalk.
Reports say the circumstances of that robbery are almost identical to last Friday’s raid.
Police have refused to rule out dissident Republicans as the culprits however.
Outlining events on the night, the report says that Detective Donohoe arrived at the credit union in an unmarked police car with fellow detective Joe Ryan, who was driving.
As was custom, they were to provide an armed escort for a credit union staff on her journey to Dundalk to deposit a bag of money at a bank night safe.
When the officers arrived at the car park, the two armed detectives realized a vehicle and four men were already waiting there.
Detective Donohoe got out of his car to question the men about what they were doing when one of them discharged a shot from a shotgun, fatally wounding him on the right side of his face and head.
he report says he was given no warning and had not drawn his sidearm.
The raiders callously continued with the robbery, shouting at Detective Ryan to stay back and threatening him at gunpoint. They also threatened the credit union staff and took a bag with the cash before fleeing.