The investigation into the murder of Det Garda Adrian Donohoe is one of the biggest ever and has involved gardai going to the US and Australia to interview suspects.
The FBI, Europol and Interpol, as well as the PSNI, police in the the UK and Holland, have been helping detectives on the case.
The garda team have gone thorugh a massive amount of CCTV coverage and a DNA sample was taken from a mallet hammer the gang left at the scene.
One of the main barriers to their enquiries has been the silence, the non-co-operation with policing in the border area that has existed since partition.
Some call it the wall of silence that exists in south Armagh, others have compared it to the south of Italy where the Mafia reign.
But the gardai are confident they will solve the murder of one of their colleagues.
“The naked reality,” Garda Commissioner Martin Callinan said, “is that there are people shielding these killers.
“They have the knowledge and we are appealing to those people to come forward.”