THE month-long investigation into the murder of Detective Garda Adrian Donohoe is winding down, with additional gardai who were drafted into Dundalk returning to their duties at other stations.
Gardai know the identity of the killer – a young man living near Crossmaglen in south Armagh – as well as his criminal associates and a 16-year-old girl who local sources have described as a "hanger-on" with the gang.
She was initially suspected of being in the car used by the gang, which has carried out a series of cross-border raids in recent years. However, it is now understood that she has an alibi for the night of the murder, January 25.
Two men, a father and son aged in their 30s and 70s, who were arrested by gardai last week are not suspected of involvement in the murder. They were questioned about a cross-border stolen-car operation before being released on Friday night.
Gardai believe that members of the robbery gang were involved in the theft and disposal of stolen cars. The Volkswagen Passat car used in the murder and robbery at the Lordship credit union was stolen from a house in Clogherhead in Co Louth two nights before the murder.
One of the difficulties facing investigators is that the main suspect lives inside Northern Ireland, which raises issues under the Republic's extradition laws.
A provision in extradition laws that dates from the 1970s, when there was a near breakdown in relations with the British government, means that the suspect cannot be questioned by gardai if he is arrested by the PSNI and extradited to the Republic.
Under the Extradition Act, a suspect has to be taken directly to court and charged once they have been extradited to either jurisdiction.
This provision dates from the time of the operation of the RUC's Castlereagh interview centre where, it was claimed, prisoners were forced to make admissions through ill-treatment.
The techniques used at the centre were heavily criticised in a 1977 Amnesty International report, which called for a public inquiry.
As a result, the Irish government refused to extradite IRA men and women who were 'on the run' in the Republic. The courts would not extradite IRA members who claimed that their alleged offences in Northern Ireland or Britain were 'political'.
After the murder of Det Garda Donohoe, Garda Commissioner Martin Callinan said that "resources will not be an issue" and that up to 150 gardai were involved in the hunt.
Two weeks into the investigation, he said 360 statements had been taken and 1,125 lines of enquiry were being pursued. Some 1,500 questionnaires had been circulated, 140 copies of CCTV footage had been taken and 300 exhibits had been examined.
The investigation does not have ballistic evidence as the murder weapon was a shotgun. The Passat car was also burned out on the road between Newtownhamilton and Keady, near the village of Darkley in south Armagh, and this would have led to the destruction of DNA evidence.
It is understood that an item found near the scene of the robbery might offer some DNA or fingerprint evidence.
At least four men were involved in the murder and robbery. After shooting Det Garda Donohoe, the gunman threatened to kill Det Garda Joe Ryan who was with him.
The gang then threatened the two credit union staff and escaped with a bag containing €4,000 in cash.
Det Garda Donohoe had arrested the gunman before and this may have been why he was murdered, colleagues say. The gunman is suspected of shooting a member of staff in the leg at a border fuel depot last November.
The gang is also suspected of carrying out at least three other robberies of credit unions in the border area and of robbing several other shops and businesses.