GARDAí conducted DNA tests to investigate whether there was a link between Graham Dwyer and the murder of teenager Raonaid Murray in 1999.
The Foxrock architect became a potential suspect in the Murray case after a text message to Elaine O'Hara described how the south Co Dublin girl's killer got away with murder.
Raonaid was stabbed to death less than 500 metres from her family home in Glenageary, Co Dublin, in September 1999.
The hunt for her attacker remains a top priority for gardaí and an incident room remains in place at Dun Laoghaire station.
Officers thought they might finally have a new lead as Dwyer was living in the area at the time of death.
The Irish Independent can reveal that detectives had Dwyer's DNA compared to samples collected during their initial investigation into Raonaid's murder.
A source close to the investigation said: "One of the first things done was to have a DNA sample from Graham Dwyer compared with one from the Raonaid Murray case but it came back negative and he was eliminated from that enquiry."
In an ironic twist, both Raonaid Murray and Elaine O'Hara had been students at the same secondary school.
The attention of the investigators was drawn to the unsolved high-profile case when they found a reference to Raonaid in a text message which was sent by Dwyer to Ms O'Hara in August 2011.