Gardai are slowly tightening the net around the suspected killers of Detective Garda Adrian Donohoe.
The father of two, pictured, was shot dead outside the Lordship credit union premises on the outskirts of Dundalk three weeks ago.
Senior garda officers said last night they were meticulously building up a case against the suspects before thinking about making any arrests.
Officers believe that a young gang of thugs responsible for a crime spree on both sides of the Louth-Armagh border was responsible for the callous shooting.
Over the past three weeks the 100-plus investigation team, based at Dundalk station and led by Assistant Commissioner Kieran Kenny, has been carefully compiling and analysing information and intelligence that has been gathered on the streets and through technological examination.
A special unit of analysts is combing through the case file and cross-referencing interviews with witnesses, the results of house-to-house questionnaires, and examining the footage taken from CCTV cameras at Lordship and the three other credit unions on the Cooley peninsula that had been targeted and put under surveillance by members of the gang in the weeks prior to the raid.
Gardai are also studying their files on previous crimes in which the killers were believed to have been involved and establishing a dossier on each gang member.
"We want to know how these people operate, who they associate with and where they have been in the weeks before and after the murder," a senior investigator said.
"It's painstaking work but everybody is fully committed to finding every piece in the jigsaw and being fully prepared before we make any moves," he added.
Commissioner Martin Callinan has reiterated his appeal to members of the public, who have information about the killers and those who helped them, to come forward and contact the gardai, either at Dundalk station or on the confidential line, 1800 666111.
Gardai have pursued more than 1,200 lines of inquiry and taken almost 400 statements.