A shotgun found at the scene of an apparent murder-suicide was legally held by the man suspected of carrying out the shootings.
The firearm was discovered next to the body of John Deegan, from Cadamstown, near Birr, Co Offaly, at a B&B in Carlow town on Monday.
Deirdre Keenan, from Kilcullen, near Naas, Co Kildare, was also found dead at the scene.
It is believed she was shot first before the man turned the gun on himself.
The pair, in their 50s, are understood to have both been separated and had been in a relationship with each other for some time.
They had been seen socialising in Carlow over the weekend and were last seen at around 10pm on Sunday night before going to their lodgings at Centaur Street in the town.
They were discovered at about 1.30pm on Monday, gardai said.
Full post-mortem examinations are taking place at Naas General Hospital in Co Kildare.