The investigation into the murder of Detective Adrian Donohoe has recorded more than 1,000 exhibits.
The father-of-two was shot in the head outside the credit union in Lordship, on the Cooley peninsula, Co Louth on January 25 as he escorted cash collections from the premises.
Garda Commissioner Martin Callinan revealed details of how the investigation was progressing as he met PSNI Chief Constable Matt Baggott at a cross border organised crime conference in Dundalk.
Mr Baggott rejected any suggestion that his officers are not prepared to pursue criminals in the south Armagh area, where the murder gang is believed to be based.
"There is nowhere we won't go to bring people to justice," he said.
"We will pursue every avenue, we will spare no resources, we will make sure we support our colleagues here as fully as we can."
Mr Callinan said that more than 3,200 statements and reports have been collated along with more than 3,600 structured lines of inquiry and more than 1,000 exhibits.
The senior officers would not be drawn on how near or far way investigating officers were from making arrests.
The annual conference is used by senior officers to discuss emerging threats and share knowledge in the context of cross border crime.
Mr Callinan said: "This is to ensure that this type of crime is, as far as possible, eliminated through effective crime prevention methodologies and ensuring all possible leads are thoroughly and professionally exhausted regardless of where it emanates from, be it north or south of the border."
PSNI Assistant Chief Constable Drew Harris said everyone has a responsibility when it comes to organised crime.
"Every time you buy dodgy cigarettes, cheap fuel or counterfeit goods, you are providing funds for organised crime. You are helping line the pockets of those involved in drugs, human trafficking and terrorism. By saying no, you can help us keep everyone safe," he said.