Notorious rapist Larry Murphy, who is the chief suspect for the murder of Deirdre Jacob, has been working on building sites in London and Birmingham as the Director of Public Prosecutions decides whether to charge him in relation to the case.
"Gardaí are aware of where Murphy is living in the London area and are aware that he has been working as a carpenter on building sites," a senior source told the Irish Independent.
In late February officers submitted a file to the DPP on the murder of trainee school teacher Deirdre Jacob, but a decision to charge Murphy has not yet been made.
In the meantime, gardaí continue to work with UK police in "discreetly monitoring" Murphy's activities there.
"The Deirdre Jacob investigation is at a very delicate stage at the moment. It is a case that is mainly based on circumstantial evidence but huge work has been put into the file," said a senior source.
"Larry Murphy is a person of interest in this murder investigation and because of this gardaí have made sure that they are aware of his location in the UK and his activities."
If the DPP decides Murphy has a case to answer, gardaí will seek a European Arrest Warrant.
The investigation is being led by Kildare gardaí under the command of Superintendent Martin Walker.
Ms Jacob (18) was last seen crossing the road towards her home at Roseberry, Newbridge, Co Kildare, at about 3pm on July 28, 1998.
Her disappearance was treated officially as a missing persons case until August 2018, when it was formally upgraded to a murder investigation.
The decision to reclassify the case followed the emergence of new information, which led to gardaí opening up fresh lines of inquiry.
One of Ireland's most feared criminals, Murphy (54), from Baltinglass, Co Wicklow, was convicted in 2001 of kidnapping, repeatedly raping and attempting to murder a young woman in the Wicklow mountains in February 2000. He was released in 2010 after serving 10 years.
On the day she went missing, Ms Jacob had left her home at around 1pm to go to Newbridge.
She was seen at the AIB bank on the Main Street at 2.20pm before crossing the street and going to the post office at 2.30pm.
The last CCTV footage of her was recorded from an Irish Permanent office on Main Street as she walked back in the direction of her home.
Murphy became a person of interest after it emerged he had visited the shop owned by Ms Jacob's grandmother.
CCTV footage from the day of Ms Jacob's disappearance has been digitalised, resulting in new witnesses being identified from the clearer video.
During an interview with gardaí while in prison, Murphy denied any involvement in her disappearance.
Gardaí travelled to the UK in 2018 and tried to interview Murphy, but he refused to answer questions.
"Murphy is an extremely talented carpenter and he has been using his skills at building sites in London and Birmingham," a senior source said last night.
"He has not come to the attention of police in the UK for any criminal offences."
Two retired detectives who secured critical testimony from a prisoner who implicated Murphy in the murder of Ms Jacob were interviewed by gardaí and their statements are included in the file sent to the DPP.