Gardaí said yesterday they had been in contact with the self-confessed British spy, Denis Donaldson, after they became aware he was living in an isolated cottage in Donegal in January.
Chief Supt Terry McGinn, who is leading the inquiry into his murder at the cottage near Glenties, said yesterday gardaí made themselves known to Mr Donaldson at that time.
"We introduced ourselves, we offered our services in terms of whatever protection he needed, so we had been in close communication with him," she said.
She declined to state if there had been any specific threats made against the former Sinn Féin administrator.
It emerged yesterday that Mr Donaldson was probably killed by two shotgun blasts while alone in the Glenties holiday cottage owned by his son-in-law.
Garda sources refused to detail Mr Donaldson's exact injuries yesterday but The Irish Times understands they were most likely caused by a shotgun and that he had not been tortured before he was killed.
An unknown number of attackers forced their way into the small property along a remote laneway about five miles from Glenties on Tuesday, gardaí believe.
A window was broken and there was evidence that the door had been forced.
The house was not ransacked, fuelling theories that the attackers sought only to find their victim and murder him.
The house is owned by Ciarán Kearney, the son-in-law of the murdered man and who was also one of the three men arrested in connection with the so-called Stormontgate spy ring affair in 2002.
Charges against all three were dropped late last year, shortly before Mr Donaldson was identified as a British agent of some 20 years' standing.
One of the largest Garda investigations ever seen in Co Donegal was under way into the killing yesterday.
Asked if republicans were suspected in the murder, Chief Supt McGinn said: "At this stage I am keeping an open mind on the inquiry and following all avenues."
The State Pathologist, Dr Marie Cassidy, carried out a preliminary examination at the scene and found that Mr Donaldson had died "from a number of gunshot blasts to the body", Chief Supt McGinn said.
The body was taken to the general hospital in Letterkenny where it is understood members of the wider Donaldson family live.
"We have been working very closely with the family of Denis Donaldson, and in close liaison with the PSNI in that regard," said Supt McGinn.
"I am now appealing to the public to assist us in bringing the perpetrators of this crime to justice," she added.
Supt McGinn said she needed the help of anyone who had been in the area in the past two days and who may have spoken to Denis Donaldson or spent some time with him.
She said there were people out there who knew what had happened. "I'm not only talking to the people in Glenties but to any other person further afield who may have seen something suspicious."
She was also unable to say how long the body had lain in the cottage before the discovery was made.
Supt McGinn said the Garda murder team was being supported by the national criminal intelligence unit.
"The Commissioner has assured me that whatever resources I need are available. No stone will be left unturned to bring these perpetrators to justice."