A post-mortem examination is underway at Mayo University Hospital on the body of a man in his 60's who was shot dead near Ballyhaunis last night.
A pathologist from the State Pathologist's office carried out a preliminary investigation earlier this afternoon at the rural farmhouse in Coogue, where the shooting took place just before midnight.
A man in his 80's is still being detained at Castlebar Garda Station in connection with the incident, and Gardai say their enquiries are continuing.
Both men were known to each other, and locals believe the deceased may have been mistaken for an intruder by the older man - but this has not yet been confirmed.
Local parish priest Fr Richard Gibbons was called to the scene in the early hours of this morning.
Speaking to Midwest News, he's described the incident as a tragedy, and says the local community has been numbed by news of the fatal shooting.