More than 360 statements and 140 pieces of CCTV are being examined by officers investigating the murder of Detective Garda Adrian Donohoe.
Garda Commissioner Martin Callinan revealed 1,125 lines of inquiry are being pursued, but warned progress in the probe will be steady and slow.
He also made a fresh appeal for information after he held a case conference with senior officers at Dundalk Garda Station, where the detective was based, exactly two weeks after the killing on the Cooley peninsula.
"The investigation is being very, very carefully worked through, it's very painstaking," said the Garda Commissioner. "The level of detail that I have received is, to say the least, extremely impressive. The structure of the investigation and the amount of people who have been interviewed to date is quite substantial.
"We have taken in excess of 360 statements, there are 1,125 structured lines of inquiry, there are potentially in excess of 300 exhibits and there are in the region of 140 items of CCTV seized."
Det Gda Donohue, 41, was shot in the head on Friday, January 25, as he approached a five-strong gang at a car in the grounds of his local credit union in the village of Jenkinstown, Co Louth.
An 08-D navy Volkswagen Passat - stolen from Clogherhead in Co Louth on January 22 and used in the attack - was later found burnt out beside a forest in south Armagh.
Last week thousands of gardai joined Det Gda Donohoe's widow Caroline, also a garda, family and friends at his funeral.
Mr Callinan said the local and wider response from the public has been terrific, and paid tribute to the Police Service of Northern Ireland for their tremendous work on the case to date. "We will work hand in glove with them," he said, revealing there were also inquiries being made off the island of Ireland.
The Garda Commissioner said there is a wider circle of people around the gang believed to be responsible for the crime but warned resources would not be an issue in tracking down the main suspects. "We're not underestimating the degree of difficulty that we face. But we are up for it and we are moving in their direction. We are not going to give up."