Convicted rapist Larry Murphy may have been in the area where student teacher Deirdre Jacob went missing 11 years ago.
Gardai have confirmed that they cannot rule out whether Murphy was in Newbridge, Co Kildare, on the day Ms Jacob disappeared in 1998.
The news came as the missing woman's father, Michael Jacob, made a fresh appeal for anyone with information to come forward.
Deirdre was last spotted in front of her family's home in Roseberry on July 28, 1998.
Murphy, the prime suspect in her disappearance, will be released in August after he was convicted of the brutal rape of a Carlow woman in 2000.
"Larry Murphy could have been working in Newbridge at the time but it has never been proved that he was working here," said Sergeant Seamus Rothwell of Newbridge Garda Station.
"We are not sure where he was that day -- the nature of his work [as a roofer] is that he would have a lot of different jobs on and we are keeping an open mind.
"We have never found where he was working on the day Deirdre disappeared. He has refused to speak to any gardai.
"His movements for July 28 have never been pinned down so we can't say either way.
"Some of the rumours about where he was working are all untrue -- he certainly wasn't working for any relations of the Jacobs.
"We'd like to know where he was working that day. We have ideas he was in the Clane area but we're struggling on his whereabouts. It was the middle of summer and the builders' holidays were on, so he may have not have been working much at that time."
Operation Trace was set up in 1998 to investigate the disappearances of six young women.
The Trace detectives found some interesting links between Murphy and the disappearances but nothing concrete.
They discovered that Murphy had been roofing a house in Newbridge around the time Deirdre Jacob went missing.
His route home from this job took him right past her house in Roseberry and along the roadway where she was last spotted at 3.30pm on Tuesday July 28, 1998.
Speaking to the Herald yesterday, Deirdre's father Michael Jacob appealed for new information and urged people to keep their minds "wide open".
Mr Jacob said that anyone with information should not presume that the culprit has been found and the case is closed.
"We are appealing for information, even if you think your knowledge is small and insignificant it could make all the difference," he said.
It is understood that gardai have already been preparing for Murphy's release and he will be watched 24 hours a day, seven days a week.
Murphy will be monitored by up to 16 detectives and the Domestic Violence and Sexual Assault Unit of the National Bureau of Criminal Investigation.