It was initially believed that James Cahillane, 58, a father of two who lived alone near Killorglin, died in an accidental fire at his home in April 2012.
However, an implement was recovered from the scene of the burnt-out home.
About 30 hours after a postmortem was conducted, a murder investigation was launched.
A Garda press conference was held in Killarney station yesterday, on the fifth anniversary of the murder. It heard that the medical examination had concluded that Mr Cahillane suffered violent blows to the body and the head. Gardaí also believe the house was set on fire deliberately.
Superintendent Flor Murphy, based in Killarney, declined to comment on whether the scene had been sufficiently preserved.
He revealed gardaí believe they have found part of the murder weapon — the head of a hammer — which was consistent with the injuries inflicted on Mr Cahillane.
They believe the hammer was brought to the house by an intruder who possibly laid in wait for the man when he returned to his home by taxi after an evening out in Killorglin.
Mr Cahillane’s daughter Lisa said yesterday: “It’s been incredibly hard. Obviously, we still don’t have any answers for this crime.
“We do really want to get some answers and so we are appealing to anyone’s conscience out there to come forward with any information they have.”
Ms Cahillane said she and her brother Gary want justice. Their father’s death, she said, is on their minds every day.
The body was discovered in the early hours of April 19, 2012. At around 2.05am, neighbours were alerted to a fire at the man’s home and the emergency services were called.
The house at Ardraw, Beaufort, was destroyed and Mr Cahillane’s body was found in the hallway of the bungalow.
A postmortem examination carried out by Dr Margot Bolster, the State pathologist, revealed the death was not an accident and a murder inquiry was then launched.
“He had been violently assaulted and his home was deliberately set on fire to conceal the crime,” said Supt Murphy yesterday.
He said gardaí have been extremely frustrated and share the frustrations of Mr Cahillane’s family over the lack of a conclusion to their extensive inquiries.
Renewed appeals often elicit necessary information, he believes, and the cold-case appeal is being screened on Crimecall on RTÉ One next Monday.
“I am convinced there are people in Killarney and the mid-Kerry area who may have information,” said Supt Murphy.
“Five years have passed and associations and loyalties will have changed.”
He appealed to people in the Beaufort area and “particularly the town of Killorglin” to come forward.
Two people, a man and a woman, were arrested at the time and are still of interest to investigating gardaí, he said. A file has been sent to the DPP but Supt Murphy said he would not disclose any details of the DPP’s decision.
There were a series of burglaries in the Killorglin and Beaufort areas in 2012, before and after Mr Cahillane’s violent death. Gardaí are examining the possibility that the killing was linked to these burglaries.
Supt Murphy said a motive may have been robbery. There is also the possibility, he said, that the victim confronted a burglar or intruder in the home.
Ms Cahillane, 34, said the past five years have been difficult for herself and brother Gary, who lives and works in Dublin.
The huge trauma of discovering their father was murdered overshadows their grief, she said.
“We can’t believe five years have gone by and we still don’t have any answers,” said Ms Cahillane.
“He was a good man, a good father, quiet, gentle, never confrontational.
Ms Cahillane acknowledged that “gardaí were doing what they could”.
She said there was nothing of great value in the house and her father would only have had some cash in his wallet. It was upsetting, she said, that in a small community, it was known arrests had been made, and there are fears such an incident could happen again.