The pair, in their 20s, left the country the day after gardai conducted the first raids directly connected to the garda’s cold-blooded murder.
Det Gda Donohoe, a father-of-two, was shot dead as he confronted raiders outside a credit union in Co Louth in January this year.
Neither man is believed to have fired the fatal shot – but they are |members of the five-man gang suspected of being involved.
However, investigations have established that the duo were in the car and, because of this, they could still be charged with murder.
But the fact that they have relocated to Australia – where it is understood that they have relatives – has made the massive Garda investigation even more complex.
A senior source said: "This is a very detailed investigation but it is also very difficult and protracted. The Gardai would like to make it clear that there will be no hiding place for these criminals, even in Australia."
This week, gardai issued a fresh appeal about the murder in which they said that the murder gang may have been seen beside a white HGV on a roadside in south Armagh just after the killing.
Officers said they want to trace the driver of the lorry and anyone who was with the vehicle on the day of the shooting at the Lordship Credit Union in Co Louth.
Gardai said the HGV may have broken down and that a number of people were seen around the lorry. They said they also want to trace anyone involved in the recovery of the lorry or servicing it.
Gardai also want to speak to anyone who was travelling on the Shean Road in the Forkhill area at around 9.45pm on the night of Detective Donohoe's murder.
Anyone with information is being asked to contact gardai in Dundalk, Co Louth.
Just a day before the suspects fled almost – on Tuesday of last week – almost 50 heavily armed gardai raided a house and farmlands in the first raid directly connected to the murder.
A number of mobile phones and laptops were seized in the dramatic top secret operation that lasted for over six hours. No arrests were made in the bust which is the first raid directly connected to the murder of the detective in the Republic of Ireland.
It all kicked off at a property near Hackballscross, Co Louth, on Tuesday and involved the heavily armed Emergency Response Unit and the garda Air Support Unit.
The specialist units were backed up by a number of tragic Garda Donohoe's detective colleagues from Dundalk.
Garda Donohoe was blasted in the head with a shotgun when he confronted a gang on rural roads near his home on the Cooley peninsula.
He had been accompanying cash lifts from the local credit unions on the night of Friday, January 25.
Gardai are reciving great help from the PSNI in the "complicated" cross-border operation and last week the PSNI raided four houses in south Armagh and seized mobile phones and documentation.
Senior sources say that the examination of CCTV evidence is playing a "huge" role in the probe.