Reports say the missing man, who is aged in his early 60s, was socialising with a woman in her 20s and a male in his 30s when he allegedly made advances towards the female, sparking the savage beating at a house in Killybegs.
The alleged attack took place last Sunday.
Gardaí became aware of the allegation after the woman at the centre of the investigation phoned a friend later, telling her what had happened. However, it is understood that this friend recorded the conversation and passed it on to gardaí.
In the recording, it is believed, the woman says the Northern Irish man was beaten around his head with a rock and his body was later dumped around the Slieve League cliffs.
This sparked a search as well as the arrest later of the man in his 30s, as well as the woman in her 20s.
Both suspects have addiction issues, according to security sources. They were later released without charge.
A car crashed in the village of Fintown last Sunday, resulting in the man’s arrest for alleged drink-driving.
The man was re-arrested on suspicion of assault as he left Letterkenny District Court, while the woman was arrested at another location.
At the same time, detectives applied to Judge Brendan O’Reilly for a search warrant to examine the man’s car. Splatters of blood were found in the car, and these have been examined and analysed by forensics officers.
A warrant was also secured to examine a property on the outskirts of Killybegs, where the trio are suspected of taking drugs and drinking together on the night of the older man’s suspected attack with a brick.
It has also emerged that the man in his 30s arrested by gardaí is the son of a well-known writer.
The couple were arrested following a tip-off and quizzed over Monday and Tuesday. They were then they were released.
The missing Northern Irish man is understood to have been staying in the Killybegs and Kilcar area before he disappeared.
Between Monday and Thursday, gardaí closed off public access to Slieve League, which at this time of year is normally busy with tourists.
The search teams involved gardaí and the Irish Coast Guard, supported by the Rescue 118 helicopter and members of the Donegal Mountain Rescue Team.
Late on Wednesday the focus of the search shifted to the nearby Teelin Pier, where the Garda Water Unit carried out searches until Thursday evening.
Gardaí have continued to exercise caution around the case, and have not even confirmed they are searching for a missing person but are only seeking information on an alleged assault at Slieve League.
If there has been a fatal assault, a body could surface in the coming days at locations around the nearby coastline.
Tags: