A man was knifed to death in a frenzied attack over a late night chess game, detectives believe.
Irish police were called to the scene of the bloody killing in a suburb of north Dublin at around 1:50am.
A 39-year-old researcher, who owned the house at Beech Park Avenue, Castleknock, was found with multiple stab injuries inside.
They believe a violent row erupted over a chess move and spiralled out of control.
Another man - aged 34 years and understood to be from Palermo in Italy - was arrested at the scene.
Investigating gardai are not looking for anyone else in connection with the death, which will be treated as murder as soon as post mortem examination results are confirmed.
A Garda source said: "It was a very unpleasant scene for our people to walk into. This was a bizarre killing and the dead man sustained substantial injuries to his body."
It is understood the dead man was a former journalist with The Voice Today, a Roman Catholic newspaper.
A graduate of University College Dublin, he was more recently a researcher with the Dublin-based Catholic lobby group the Iona Institute.
The man - who has a brother and a sister - was living at the family home after his mother died in 2012. His father had also passed away.
He is believed to have taken in a lodger in recent months to help supplement his income.
It is not thought there were any drink or drugs involved in the incident.
A knife has been recovered at the scene.
The arrested man has been taken to Blanchardstown Garda station where he is being held under section four of the Criminal Justice Act.
He can be detained for up to 24 hours and detectives have until tomorrow morning to charge or release him.
The scene has been sealed off for a full technical examination by forensic experts.
State Pathologist Marie Cassidy has been asked to carry out a post mortem examination at the City Morgue.
The latest killing is the fifth in Ireland over the past week.
In a separate incident, two men remain in custody over the death of a 29-year-old man at a house party in Finglas, north Dublin, on Saturday morning.
Investigating gardai are seeking revellers who were at the gathering in the ground- floor flat at Spring Mount Apartments in Wellmount Road on Friday night and Saturday morning.
The man killed at his home in Castleknock was named locally as Thomas O'Gorman.
In a statement, David Quinn, director of The Iona Institute, said Mr O'Gorman's friends and colleagues were devastated at his death.
"On behalf of everyone at The Iona Institute, I would like to express our total shock and deep sorrow at the terrible and untimely death of Tom O'Gorman," he said.
"Tom was a friend as well as a work colleague to us all."
Mr Quinn confirmed Mr O'Gorman had been working as a researcher at the Iona Institute for the past seven years.
"Most of us knew him from before then, in some cases all the way back to his days at UCD," he said.
"He was a fond and dear friend and we will all miss him.
"We extend our deepest commiserations to his family and above all to his sister and brother, Catherine and Paul."