Former journalist Tom O'Gorman, 39, who owned the house in Dublin where he died, was found with multiple stab injuries early yesterday morning.
Saverio Bellante, 34, originally from Palermo in Sicily but with an address at Beechpark Avenue in Castleknock where the killing took place, appeared before Blanchardstown District Court on Monday.
Detective Garda Patrick Traynor told the court that when charged and cautioned on Sunday, the defendant replied: "I am guilty."
It is understood he had been playing chess with Mr O'Gorman when a row broke out.
The alarm was raised at about 1.50am on Sunday and two uniformed officers called to the house to find Mr O'Gorman dead.
Bellante is charged with his murder.
During the brief district court hearing Detective Traynor said Mr Bellante was charged by Garda Sergeant Morgan O'Connor on Sunday night.
"He was cautioned. His reply of the caution was 'I am guilty'," Detective Traynor told the court.
Mr O'Gorman was a former journalist with The Voice Today, a Roman Catholic newspaper.
A graduate of University College Dublin, he had worked for the past seven years as a researcher with Dublin-based Catholic lobby group the Iona Institute.
Mr O'Gorman - who had a brother and a sister - was living at the family home after his mother died in 2012. His father is also dead.
Tom was a friend as well as a work colleague to us all.
David Quinn, The Iona Institute
Dressed in a black jumper and black trousers, Mr Bellante told the court in a strong Italian accent that he would represent himself.
Judge David McHugh asked Mr Bellante to clarify whether he wanted legal representation and he replied: "I was asked if I wanted to represent myself and the answer is yes."
Mr Bellante was remanded in custody to appear before Cloverhill District Court in Dublin on 17 January.
Judge McHugh also directed that he undergo a medical assessment while in custody.
Police have said some of the details of Mr O'Gorman's death and the circumstances of the arrest of Mr Bellante are too horrific to release.
It is understood the Italian man had been living in the house as a lodger as Mr O'Gorman sought to supplement his income in recent months.
It is not thought there were any drink or drugs involved.
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.
Mr Quinn said that Mr O'Gorman had been working as a researcher at the 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."