GARDAI leading the hunt for the killers of their colleague, Adrian Donohoe, believe a child car seat and a specialised hammer may be vital evidence in the case.
An increase in the reward for information leading to the capture of the murderers was also announced as gardai put the seat and hammer on display.
The investigation has followed up more than 2,300 lines of inquiry and more than 800 people have been interviewed since Detective Garda Donohoe was shot dead on January 25 outside the Lordship credit union near Dundalk, Co Louth.
Officers issued an appeal for assistance in tracking down the seat, which had been fitted to the VW Passat car used by the five-strong gang.
The green-coloured 'Cosatto' seat, which is suitable for an eight or nine-year-old, was not in the car when it was found burnt out at Cumsons Road, Newtownhamilton, Co Armagh.
Officers are satisfied that the graphite blue 08 D-registered automatic car was set on fire around 10.30pm, about an hour after the murder. It was found in the early hours of Sunday, January 27. Gardai are now trying to establish if the seat was dumped somewhere or offered for sale.
The high-backed booster seat carries a 'Little Monster' motif and costs €119. It was described as "almost new".
Gardai also want to know where the car used in the raid had been stored after it was stolen in Clogherhead, Co Louth, either on January 22 or 23.
And they are trying to trace the history of a precision mallet-type hammer, which was used by the gang to smash the windows of the cars used by the credit union officials. Recovered at the scene, it has a black rubber handle with a red painted section and soft rubber head.
The hammer used by the gang was missing a hard plastic section and had a steel screw protruding. It also had significant wear marks on the red paint of the handle.
Assistant Commissioner Kieran Kenny, who is spearheading the investigation, confirmed there were five gang members at Lordship when Det Gda Donohoe, a father of two, was shot dead with a long barrelled shotgun.
Gardai believe some gang members were not aware a garda was to be shot and they are anxious the gunman's associates contact them, either at Dundalk station, or on the confidential line, 1800 666111.
A reward of €50,000 for information has already been offered by the Irish League of Credit Unions and Crimestoppers has added a further unspecified five-figure sum.