Gardai are to question the girlfriend of one of the main suspects in the Detective Garda Adrian Donohoe murder in Dundalk.
The woman, in her early twenties, fled Ireland to be with her partner in the aftermath of the murder four years ago this week.
It is understood she and her partner and his brother, also a suspect in the murder gang, were living in Massachusetts and New York.
The suspect brothers' relatives are millionaire fuel and cigarette smugglers closely linked to the Provisional IRA in the Cooley Peninsula area. They have been able to protect and finance the brothers, and are related on their mother's side to a well-known Irish Traveller family with business interests in New Jersey. The brothers are believed to have stayed there as well.
It was reported the brothers and the young woman attended lavish social gatherings.
However, all three were illegally in the US and when she was detained after a road accident in October the young woman went into the Federal deportation programme and arrived home last weekend.
She is staying with her parents, described by local people as an 'honest' couple with no criminal or paramilitary connections.
There were five members of the gang on the night of the murder in January 2013. The young man who is suspected of shooting is also believed to also have been on the run in the United States and was detained briefly in New York but released. It is believed he has travelled back and forth to the US on a number of occasions.
All the gang members have either family or criminal associations with the South Armagh IRA. One is a nephew of the man believed to be a violent Provo smuggler closely linked to another local Provo boss responsible for ordering the murder of innocent local man, Paul Quinn (21) in October 2007.
Garda sources say that while the gang, all in their late teens or early twenties, were involved in small-time armed robberies they were all working their way up the criminal ladder of the South Armagh Provo operations.
It is believed they were intending to raise a €30,000 'buy-in' to one of the Provo cigarette smuggling operations.
They escaped with €4,000 in cash during the robbery of the Lordship Credit Union in Dundalk and had carried out a series of similar robberies along the Border, including one on a fuel depot two months earlier in which an innocent Polish employee was shot in the thigh and was fortunate not to have bled to death.
It is believed the same shotgun that killed Det Garda Donohoe (41) was used in this robbery.
After the murder the gang drove a stolen VW Passatt into south Armagh and burned it near the village of Darkley. The gang had been living nearby in the Cullyhanna area, in the heart of the IRA's smuggling territory.
Two of the gang have remained in south Armagh, one frequently crossing the Border smuggling fuel and cigarettes for the IRA. Another moved temporarily to north Armagh but later returned. He, too, is linked by family to notorious Provo smugglers.
Last week Garda Commissioner Noirin O'Sullivan issued a statement praising the efforts of gardai who have been investigating the murder.
No charges have yet been brought but sources say they are still 'hopeful' of bringing charges. Commissioner O'Sullivan said: "Extensive inquiries continue to be carried out in this country and with our international partners, including the PSNI. This is a highly complex investigation and it is important that as with all such investigations that we make sure we have every single detail right."
Gardai suspect two of the gang involved in Det Garda Donohoe's murder were also involved in a cross-Border incident before last Christmas in which six PSNI officers and two gardai were injured when their cars were rammed by the gang. Police sources say the gang is now involved in cocaine smuggling.