An investigation into the murder of a former dissident republican, Seamus McMahon, in Dundalk at the weekend has spread across the border.
Senior gardai are liaising with the PSNI in a bid to find clues to the identity of the killers of 41-year-old McMahon.
The PSNI are helping in the search for a white hatchback car, either a Toyota Corolla or a Nissan Almera, which was used by the gang in their getaway at the Bothar Chroinn estate in Saltown, Dundalk, on Sunday night.
The two police forces are sharing intelligence on the known movements of dissidents and criminals in the border region around the time of the fatal shooting.
It is not yet clear whether Mr McMahon was a victim of former republican associates or criminal factions when he was shot twice in the chest in the bathroom of a friend's apartment at Bothar Chroinn.
Mr McMahon, who is the father of a 15-year-old boy and from the Green Acres area of the town, died soon after being admitted to Our Lady of Lourdes Hospital in Drogheda.
Gardai believe he may have been targeted because of his involvement as an "enforcer" for crime gangs.
But they are also investigating the possibility his murder could have been linked to a row, which resulted in him breaking his link with the Continuity IRA.
So far, gardai have found no trace of the handgun used in the shooting.
Officers are examining footage taken from CCTV cameras in business premises along the possible escape routes used by the gang.
Gardai are satisfied the two killers made their getaway by climbing over a wall and fences on to the front of the estate where an accomplice was waiting in the white hatchback car, which left in the direction of the Fatima estate.
Mr McMahon had previously been acquitted by the Special Criminal Court on a charge of membership of the IRA.
Last month he and another suspect from Dundalk were arrested by gardai investigating a violent break-in in Mayo.