Gardai are investigating if a member of a notorious Crumlin crime family shot and killed Trevor Deely before dumping his body in a Dublin wooded area almost 17 years ago.
Detectives recently received information which alleges that Mr Deely, who was 22 when he disappeared in December 2000, was shot before his body was dumped in west Dublin.
A three-acre wooded site in the Chapelizod area has been sealed off to facilitate an extensive garda search.
The information was received from an informant in recent months, who has alleged that a well-known Crumlin criminal is responsible for Trevor's murder.
However, senior sources last night stressed that there were "certain doubts" in the statements they have received, while adding that the information had to be acted upon.
"While there are certain doubts in this case, gardai were given an account of what happened to Mr Deely and where his remains were buried," a senior source said last night.
Mr Deely was last seen on the morning of December 8, 2000, in the Haddington Road area of the city centre.
The information recently passed to gardai was not as a result of their public appeal earlier this year.
The individual who has given information to gardai has not supplied any motive for the alleged murder of Mr Deely, but claimed that he was killed after having an interaction with the Crumlin criminal on the morning of his disappearance.
The alleged suspect, who cannot be named for legal reasons, is a well-known criminal who has been involved in various forms of criminality over decades.
He is a convicted drug dealer who has operated in the south inner city and south Dublin areas.
His family has also been involved in a litany of crimes, including firearms offences and the sale and supply of drugs.
Two of his siblings, who were involved in criminality, are now deceased.
Associates of the alleged suspect were involved in running street prostitution in the Baggot Street area at the time of Mr Deely's disappearance.
This criminal gang have also been investigated for the unsolved murder of 21-year-old prostitute Sinead Kelly in the same locality in June 1998.
Ms Kelly, from Santry in Dublin, was brutally stabbed to death on the banks of the Grand Canal off Baggot Street on June 22, 1998.
Gardai believe that she was murdered because she owed IR£800 to a Dublin drug dealer.
Two files, one on him and one on the man whom detectives believe he hired to kill Ms Kelly, were sent to the Director of Public Prosecutions.
However, the DPP decided that there should be no prosecution in the case.
Speaking at the Chapelizod search site sealed off over the weekend, Det Insp Paul Costello said that gardai would be keeping an "open mind" as the examinations developed.
"The reason for this is because we're conducting a search over the coming days, searching for evidence connecting to the disappearance of Trevor Deely," he said.
"I'd like to take this opportunity to appeal to anybody who has not come forward to contact us at Pearse Street Garda Station or on the Garda Confidential Line. You will appreciate that this is a very stressful time for the Deely family, and I'd ask that their privacy is respected."
A number of specialist garda units are also assisting with the search.
Mr Deely's case was never closed and a dedicated unit operating from Pearse Street was set up last December to carry out a complete review of his disappearance.
In April, newly-enhanced CCTV footage was released showing Mr Deely talking to a man dressed in black outside the Bank of Ireland on Baggot Street.
Detectives believe this was the same man captured on CCTV following Trevor along Haddington Road afterwards.
The individual has never come forward to make contact with gardai.