The 25-year-old son of a woman found dead in the family home in Cork City was being questioned by gardaí last night.
Paul Horgan was arrested at his home on Murmont Ave, Montenotte, after neighbours raised the alarm following the incident yesterday morning.
He was taken to Mayfield Garda Station for questioning where he was being detained last night under section 4 of the Criminal Justice Act.
Marian Horgan, 60, received fatal injuries in an incident in her home, while her husband, 67-year-old Billy Horgan, was seriously injured.
Gardaí have confirmed that they have launched a murder investigation, following the completion of a post mortem examination.