GARDAI investigating the murder of Elaine O'Hara are understood to have identified a man they believe was in contact with the victim just before her disappearance.
It is understood that the man was known to Ms O'Hara and met her through a specific website that they both used.
The breakthrough by detectives at Blackrock garda station was made following analysis of Ms O'Hara's second mobile phone, which was recovered along with her keys in Vartry reservoir in Co Wicklow last Tuesday.
However, gardai refused to comment about the progress in the case, with one source revealing that investigators "have a huge amount of work yet to do" to catch the killer.
Officers are still trawling through hundreds of hours of CCTV footage from areas of south Dublin Ms O'Hara used to frequent before she vanished on August 24 last year.
Detectives, under the command of Chief Supt Diarmuid O'Sullivan, are currently compiling a list of everyone who came into contact with the murder victim up to four months before it is believed she was murdered by someone she knew.
So far officers have been interviewing people who used the same website and are compiling detailed dossiers on up to five men. But one individual in particular has become of particular interest.
The search of an area in the Killakee Woods where the remains were first located last Friday week was officially called off by gardai in Rathfarnham on Saturday.
But they are continuing to preserve the scene pending the need for a further search as the murder probe progresses.
Detectives have been interviewing friends of the 36-year-old childcare assistant in the belief that she may have confided in someone about the relationship she was having with the man.
Data recovered from Ms O'Hara's mobile phone has proved crucial to the investigation because it has emerged she used it for her private contacts.
Gardai also believe she had the phone with her at the time of her death. Detectives are understood to have recovered records of her phone calls, along with locations in which the phone was last used.
CCTV footage from all those locations is also being currently examined in the hope of capturing footage of Ms O'Hara in the man's company.
The murder victim, who lived in Stepaside, Co Dublin, was described by gardai as extremely vulnerable and had been discharged from hospital where she was treated for depression the day before she vanished.
Ms O'Hara had been deeply affected by the death of her mother a number of months before. Her distinctive 05 Fiat Punto car was found parked at Shanganagh Cemetery, where her mother was laid to rest, three days after she went missing.
Gardai are trying to piece together the sequence of events that took place after Ms O'Hara was last seen in Shankill on the evening of August 24, 2012.
It will be crucial to identify the location where she met her death and how she was killed.
Detectives then have to unravel the mystery of how her body was dumped in dense undergrowth in the foothills of the Dublin Mountains while her personal belongings were thrown into Vartry Reservoir.
The work of a uniformed garda from Roundwood station is being credited with helping to make the breakthrough which is likely to lead to the capture of a dangerous killer.