ADRIAN Donohoe's killers have been given a tough no-nonsense warning by the Garda Commissioner – keep looking over your shoulder.
Martin Callinan said they should now give themselves up before gardai come "knocking on the door".
The sheer scale of the investigation into one of the most high-profile garda murders in the history of the State was made clear by Commissioner Callinan at a special press briefing in Dundalk.
He said that gardai have scoured through some 400,000 hours of CCTV footage, have taken more than 2,100 statements, and gathered more than 1,200 exhibits.
They have also sought international assistance as part of their inquiries.
However, "ordinary everyday people" both north and south of the border, have hampered efforts to capture the killers, by refusing to come forward with crucial information.
The Garda Commissioner said some may be living in fear for their own safety, which is "understandable to a degree".
But he assured those who are in a position to help the gardai that "no stone will be left unturned" in terms of their protection.
"We will look after anybody that comes forward to us with information – and we will do that very forcibly," he said.
"People are shielding the murderer and I'm appealing for them to come forward. They know what these people did on the night, before and after.
"I'm making a heartfelt plea to come forward and help us – so that we can progress the investigation even faster."
Mr Callinan said they have a "choice to make" as to what type of society we want to live in.
"Is it acceptable that people can go around murdering one another, and murder a member of an Garda Siochana, who's charged with the responsibility of upholding the law," he said.
And he warned those who are threatening people with vital information they will be dealt with "very severely".
Speaking directly to Garda Donohoe's killers, he warned that gardai are keeping a "very good eye on the target", adding that they know the identity of the gang members.
He also paid special tribute to the PSNI, along with Dutch police and the FBI, who are assisting in the investigation.
"We have sent officers to a number of these countries to try and gather intelligence and evidence," he said.
"All of these law enforcement communities have been particularly useful to us. It's a huge and complex investigation and we are following all avenues of inquiry."
He also vowed to plough as much resources as are necessary into the investigation until those responsible are caught.
"There is no question of resources being wound down in terms of work... whatever resources are required will be at the disposal of colleagues here at Dundalk."
The father-of two was shot dead on the evening of January 25 last year when a gang of cross-border criminals robbed a credit union in Lordship, near Dundalk, Co Louth.
It is understood some of the suspects in the five-man gang have fled the country.