Gardaí have officially upgraded a missing persons inquiry to a murder investigation as they believe there is no evidence that William Delaney is alive.
Garda Chief Superintendent John Scanlan is leading an investigation team which met for more than two hours on Monday to review last week's search and arrests.
He confirmed that investigations are ongoing in what is now a murder investigation. Other possible causes of death have not been ruled out.
“There are no viable signs available to the inquiry to show that William Delaney is still alive,” he said.
Mr Delaney has been missing since January 31.
Gardaí are following a number of lines of enquiry a week after a search between Portlaoise and Stradbally looked like it would lead to the discovery of his remains.
Despite the emergence of what appeared to be reliable evidence that William Delaney had been killed, his remains were not found following a four-day search which concluded last Friday evening at the Rock of Dunamaise.
No admissions emerged from the questioning of two people who were arrested under suspicion of murder.
The search began and arrests were made after a recording containing an alleged admission was reported to Gardaí in Portlaoise. The evidence also pointed to the Rock of Dunamaise as the location where remains were buried.
A garda search team was immediately deployed last Tuesday, June 18. The Garda helicopter also spent most of the afternoon hovering over the Portlaoise area.
However, no evidence was immediately found but, because the evidence provided appeared to be definitive, gardaí decided to comb a wide area around the historic Laois landmark.
Members of the Irish Defence Forces were called in on Wednesday morning. Up to 60 Army and garda personnel were on duty at one point during the search.
The search would continue through to Friday and extended up to the walls of the castle.
Thursday marked what appeared to be a significant development in the investigation when arrests were made.
A man, aged in his 30s, who it is believed is directly linked to the recording which led to the search, was arrested and brought to Portlaoise Garda Station for questioning.
A young woman who is aged in her late teens, was arrested at the same time. She was brought to Tullamore Garda Station for questioning.
She remained in garda custody until Saturday morning while the man was not released until Saturday evening. A health issue interrupted his period of detention. He was taken to the Midland Regional Hospital Portlaoise.
William Delaney's family were at the Rock of Dunamaise as Gardaí moved in to begin the search last week.
“We're fearing the worst. It is a hard emotional thing to take in,” said John Paul.
He said the family was worried how William may have died if he is dead.
He hoped the search and the Garda investigation would lead to truth.
“We need answers. We are entitled to that after five months. Our dad is probably lying somewhere. We need someone who done this to come forward. It is the least they can do and show the gardaí where he is so we can bring him home and lay him to rest.
Gardaí appealed to anyone with information to come forward with any detail that could help in establishing Mr Delaney's whereabouts. Mr Delaney was reported missing from his home in Fieldbrook, off Portlaoise's Dublin Road on Wednesday, January 31. He was originally a native of Tipperary.
He is described as 5" 6, with medium build, black/grey hair and blue eyes. Is it not known what he was wearing when last seen.
Anyone with information is asked to contact Gardaí at Portlaoise on 057-8674100, the Garda Confidential Line on 1800 666 111 or any Garda Station.