The Irish League of Credit Unions has offered a reward of €50,000 for information that leads to arrests and prosecutions in the case of Detective Garda Adrian Donohoe, who was shot dead during a raid on Lordship Credit Union in Co Louth on Friday night.
The announcement was made on RTÉ's Crimecall where gardaí renewed their appeal for information about the killing.
Superintendent David Taylor said they were seeking information on the movements of a navy Volkwagen Passat, with a 08D registration, that was found burnt out in south Armagh on Sunday.
He said the car was taken during a burglary in Clogherhead in Co Louth on Tuesday night, 22 January or in the early hours of Wednesday morning, 23 January.
Detectives believe the car remained in the area days before the armed robbery.
Gardaí have issued an appeal for anyone who may have seen such a car to contact the incident room in Dundalk.
It has also emerged that Garda Donohoe was not due to be on duty last Friday night, but was filling in for a colleague.
Detectives say the gunman did not hesitate before shooting the 41-year-old garda in the head.
The killing and robbery took place at the Lordship Credit Union in Bellurgan, Jenkinstown in Co Louth on Friday night.
The investigation into the murder is focusing in on a cross-border gang.
Detectives are examining CCTV footage taken from local businesses, petrol stations and the credit union.
Detective Garda Joe Ryan, who was held at gunpoint during the robbery, remains deeply traumatised.
The road at Bellurgan was re-opened today and wreaths were laid at the credit union in memory of Det Donohoe.
A minute of silence was observed at Dundalk Circuit Court.
The Cabinet has been briefed on the garda investigation.
Meanwhile, books of condolences remain open in several garda stations around the country and at the Mansion House in Dublin.
The remains of the father-of-two are reposing at his home today ahead of his State funeral tomorrow at St Joseph's Redemptorist Church in Dundalk.
Minute's silence observed in the Dáil
A minute's silence was observed in the Dáil as a mark of respect following the murder of Det Garda Donohoe.
The Taoiseach said that today the nation speaks as one on a man murdered in the service of his community and his country.
Enda Kenny described Det Garda Donohoe as a precious husband, taken from his wife, and an adored father, taken from his children, a deeply loved son, reared to be loyal to his community, his people, and his country.
Tánaiste Eamon Gilmore said the murder showed that gardaí were not just the guardians of the community, but also the pillars of the community.
He said Mr Donohoe had lived by the ideals of public service.
Minister for Justice Alan Shatter said he had been shocked to receive the call on Friday night informing him of the murder.
He said the public regarded an attack on a member of the force as an attack on the community and the State.
Fianna Fáil leader Micheál Martin said people must work together to bring those behind the crime to justice.
Sinn Féin leader Gerry Adams said Det Garda Donohoe had died in the defence of other citizens.
Mr Adams said that his death provoked memories of the killing of Jerry McCabe by the IRA in June 1996.
He apologised to Mrs McCabe, the McCabe family and to Garda Ben O'Sullivan, who survived the shooting.
Mr Adams also apologised to other members of what he described as "State forces" who were killed by Republicans in the course of the Northern Ireland conflict.
Speaking on behalf of the Technical Group, Mattie McGrath said the murder was an unspeakable tragedy.