A new witness has come forward with information that supports the gardaí's belief that long-term missing man Trevor Deely was murdered after an altercation.
Gardaí have been following a line of inquiry that Mr Deely - who will have been missing 19 years this Sunday - got into a row with a criminal gang on the night he disappeared in Dublin.
A senior source said last night that this new witness is "highly significant" and strengthens that theory even further. The person, whose sex has not been disclosed by investigating officers, came forward last month.
"This is a highly significant new witness, who is backing up information that Trevor was the victim of foul play on that night," a senior source said last night.
"The information supports the main theory that Trevor interacted with a serious criminal gang who were operating on the Grand Canal at the time, and got in an altercation with them.
"There is nothing to suggest that this new witness is not credible - the account feeds into other information that gardaí have got over the years.
"The belief is that this unfortunate young man was murdered at the location and his body dumped elsewhere."
Mr Deely, a Bank of Ireland worker, was last seen in the early hours of December 8, 2000, in the Haddington Road area of the city. The last known images of him were captured by a CCTV camera at the junction of Haddington Road and Baggot Street at 4.14am.
A man dressed in black, who gardaí believe also spoke to Mr Deely outside his place of work minutes previously, can be seen following him in the direction of Haddington Road.
This footage was only made public earlier in 2017 after a specialist unit, set up in Pearse Street garda station to review the case, secured improved CCTV images.
This specialist unit is now dealing with a number of leads, including a key witness who had not previously come forward.
It can also be revealed that investigators at Pearse Street believe some of the protagonists, and others who have knowledge of the suspected murder, have died since the mystery disappearance.
Gardaí would not be drawn on why the witness took so long to come forward, despite repeated appeals for public information over 19 years.
"Everything can change over time - allegiances change, people die, people fall out - all these things can be factors," the senior source explained.
"Witnesses who come forward with information must be treated in a very sensitive way.
"The hope now is that this new information may lead to a breakthrough in the case, because that poor family have suffered enough."
In August 2017, it emerged that an informant alleged that a member of a dysfunctional crime family shot and buried Mr Deely, and they said they came forward due to a guilty conscience.
At the time, the criminal told investigating detectives he had no interest in the €100,000 reward being offered for any significant information in relation to Mr Deely's disappearance, but instead said he could not keep the information a secret any longer.
This led to a massive six-week dig in the autumn of 2018 at a site in Chapelizod, west Dublin, which turned up nothing of relevance to the case, but a gun and drugs did show up in the area.
Mr Deely went missing as he was making his way home from the bank he worked in following a night out at a Christmas party with work colleagues.