Gardaí are seeking to piece together the movements of convicted rapist and murderer Robert Howard since the early 1980s to see if he might be connected to the disappearance of a number of women in the State.
Howard (61), of Wolfhill, Co Laois, was sentenced to life imprisonment in October 2003 for the murder of English schoolgirl Hannah Williams.
Reporting restrictions on his conviction were lifted only yesterday after outstanding charges against him in connection with the murder of Co Tyrone teenager Arlene Arkinson were dropped at Belfast Crown Court.
Detectives investigating the disappearance of several women in the Republic are examining whether evidence from the Williams case can shed light on their inquiries.
However, they have no specific evidence linking him with any of the disappearances.
Howard travelled extensively between Ireland and the UK after leaving Mountjoy Prison in 1981, living in Monaghan, Letterkenny and Wexford.
While in Dublin, he resided in Ranelagh, Coolock and Clondalkin at different times.
A chief suspect in the disappearance of 15-year-old Arlene in 1994, Howard was investigated by detectives under Operation Trace.
This was the special inquiry which was set up in 1998 to attempt to locate a series of women who had gone missing in the Leinster area in previous years.
In 2002 gardaí and the RUC met to discuss Howard's activities, but no connections were made to other missingperson cases.
Gardaí said that while Operation Trace had wound down, the individual cases at the centre of the operation were still being investigated.
Meanwhile, Arlene's family expressed renewed disappointment yesterday about Howard's acquittal for the murder of the Co Tyrone girl.
The victim's sister Kathleen said: "The law has to change. That jury would not have acquitted him if they had known his background."
Howard was found not guilty of killing Arlene at Belfast Crown Court in June.
The rapist was already serving life in jail for murdering Williams (14) of Deptford, south-east London, in 2001.
With reporting restrictions now lifted after other sex offence cases were dropped, Kathleen Arkinson said that she was still astonished that the prosecution failed.
"It's unreal, I just don't know how this could happen," she said.
"But we are happy that people will know the truth about him.
"If a person like that ever comes into a community, people need to know about it. No child and no woman is safe from him."
Despite major police searches, the schoolgirl's body has never been found.
However, her sister refused to give up hope that the family will eventually be able to give her a proper burial.
"We have another search coming up before Christmas near Castlederg," Ms Arkinson said.
"It's so sad that we can't find Arlene's remains, but we are going to continue until we find her."
