THE 'Bandit Country Omerta' of south Armagh is protecting the killers of Det Garda Adrian Donohoe, gardai believe.
Not one witness who could give vital or even circumstantial evidence has come forward in the area north of the Border as the first anniversary of the detective's murder approaches.
Gardai say they and the PSNI ran into the same brick wall during the investigation of the October 2007 murder of 21-year-old Paul Quinn, who was beaten to death by the south Armagh Provisional IRA. In that case also, not one material witness came forward.
Fear of being branded an informant, with the likelihood of being murdered or forced into exile, is preventing people who could help solve the detective's murder on January 25 last year from coming forward, sources close to the investigation say.
And they say part of the blame lies with Sinn Fein's failure to promote proper policing of the Bandit Country area, where smuggling and other crime still flourish. Normal day-to-day policing has never been established in the area, with the only station in Crossmaglen still hidden behind the high blast walls that protected it from IRA bomb and rocket attacks during the Troubles.
All four main suspects for the robbery in which Det Garda Donohoe was shot dead have been living just north of the Border, although three have spent time in the United States since the murder.
Two of the suspects are related, both in their 20s, who have been in the United States since last year. They are due to return home when their 90-day visitor visas run out.
Their family home is in the border area north of Dundalk, where the detective was murdered. However, since the murder, they had been staying north of the Border before they travelled to the US.
The two come from a family of fuel smugglers and are suspected of being involved in a number of robberies in the border area before Det Garda Donohoe's murder.
Detectives travelled to Boston last month and made contact with the two, inviting them to attend an interview in a Boston police station. The pair refused to comply.
The man suspected of firing the shotgun that killed Det Garda Donohoe also travelled to the United States in the weeks after the murder but returned home last summer when his visa ran out.
He lives just north of the Border, in an area south of Newry. He has relatives based in the east coast of the US, with whom he stayed while in America.
While this man was in the US, gardai travelled to New York and liaised with the FBI last July. The suspect was asked to present himself for questioning, but he refused to do so.
The fourth man who gardai suspect was in the car during the robbery of the Lordship Credit Union in Dundalk is also living in the Crossmaglen area of south Armagh.
His family has strong republican links and gardai do not believe that anyone in the area with information would be prepared to help the investigation.
Gardai and, to a lesser extent the PSNI, received very considerable amounts of information on a confidential basis in the early part of the investigation but no potential witness was prepared to come forward.
Detectives have amassed significant information gleaned from mobile phone traffic on the night of the murder. It is likely that there will be further arrests and the suspects will be asked to account for the movements of their phones during the relevant periods.
Last year, the PSNI questioned a teenage girl from the border area, the girlfriend of the man suspected of firing the fatal shot, after she had initially provided alibi testimony that she was with the suspect on the night of the murder. She has since declined to make any further statement.
A cousin of this main suspect is currently wanted by the PSNI for questioning about a break-in at the home of a PSNI officer in the Newry area last November.
He is a member of the same gang but was not present on the night of the murder. He is also suspected of having stolen the black VW Passat that was used in the robbery and murder of Det Garda Donohoe.
Investigators have been in constant contact with the Director of Public Prosecutions office, trying to establish the point at which they have a case based on available, mainly circumstantial, evidence to bring charges. Only at that point, sources say, will arrests be made and the suspects questioned.
The suspected gunman and his accomplices have already furnished the PSNI with statements via solicitors, denying any involvement in the murder. This is standard practice in Northern Ireland in criminal cases where a suspect's refusal to answer questions can be taken into account as an inference of guilt.
The last man to give evidence in an open court about the IRA's operations in south Armagh was 45-year-old former IRA man and author Eamon Collins. He was subsequently beaten to death by the IRA while walking his dog in the countryside near his home in Newry.