Senior officers last night said a file would be sent to the Director of Public Prosecutions in the coming weeks.
Ms O’Reilly, a 30-year-old mother of two children was found beaten to death at her home in Naul, north Co Dublin, on October 4, 2004.
Detectives were able to rearrest the man after producing new evidence to the courts.
The evidence includes:
* An analysis of the suspect’s mobile phone records, which appear to clash with the suspect’s supposed movements on the day of the murder;
* A “blood splatter analysis” from the scene of the murder;
* New imagery of the clothes used by the accused on the day of the murder;
* New imagery of the car driven by the suspect on the day.
Gardaí arrested the man at his home in north Dublin at around 9am and detained him under Section Four of the Criminal Justice Act.
He was released last night after his 12-hour detention period came to an end.
At around 4pm, officers had rearrested the man’s girlfriend, again on suspicion of withholding information.
She was detained under section 30 of the Offences Against the State Act, and can be held for 24 hours. She was still in custody last night.
Senior officers last night said a file would “definitely” go to the DPP.
“It’s nearly complete. It will go in three to four weeks,” said one source.
Gardaí are believed to have traced the location of calls on the suspect’s phone close to the home of Ms O’Reilly on the morning of her death.
These appeared to clash with the account given by the man, who claims he was not near the house at the time.
Yesterday’s arrests are the fifth since Ms O’Reilly was murdered. A third person, who is providing an alibi to the main suspect, was arrested last year.
Gardaí searched three properties yesterday on foot of a warrant from Balbriggan District Court, while forensic experts carried out analysis at the scenes.
A post-mortem examination found Ms O’Reilly died after being struck with a blunt instrument, which so far hasn’t been found.
Yesterday’s arrests coincided with the reopening of the inquest into Ms O’Reilly’s death at the Dublin County Coroner’s Court.
Inspector Oliver Keegan from Balbriggan Garda Station asked the coroner, Dr Kieran Geraghty, for a six-month adjournment as investigations into Ms O’Reilly’s death were continuing. The inquest was adjourned until September 5.