The three were named in a file sent to the Director of Public Prosecutions as the suspected killers of Joseph Vickers, whose badly beaten body was found on a beach in Wicklow nearly three years ago.
But the DPP decided this week not to bring the suspects before a court.
Mr Vickers, a 43-year-old convicted drug dealer originally from Bray, had been living in a caravan close to Greystones North Beach for two months prior to his death in December 1999.
The partially clothed remains of the victim were discovered near the caravan by fire crews. The crews had arrived to tackle a blaze at the caravan, which was parked close to the beach.
The garda who headed the murder investigation was reluctant to comment about the DPP decision.
Garda Superintendent Phil Moynihan said: “The DPP decided that there was not enough concrete evidence. It is disappointing, as we thought that there was enough.”
A team of up to 40 detectives and uniformed gardaí worked on the case and within days of the body being found, Supt Moynihan was able to report the team was following definite lines of inquiry.
In the weeks following the killing, nine people - five men and four women - were all arrested within the Bray area.
Mr Vickers died following a frenzied attack, suffering multiple injuries to his head and body.
There was speculation his death was drug-related. The Bray man served five years of a seven-year sentence for drugs offences. He was released in 1997.
An extensive search failed to locate the murder weapon or weapons, one or more blunt instruments used to beat the victim.