A man has been arrested on suspicion of murdering Josephine “Jo Jo” Dullard, gardaí (Irish police) have said.
The 21-year-old went missing from Moone in County Kildare in 1995.
The case was upgraded from a missing persons to a murder inquiry in 2020.
Investigating officers have also commenced a search operation on open ground, at an area near the Wicklow/Kildare border.
“This area of land will be searched and subject to excavation, technical and forensic examinations over the coming days,” Supt Paul Burke told reporters on Monday.
The arrested man, who is in his 50s, is being held at a Garda station in County Kildare.
It is the first arrest in the case.
Gardaí also searched two properties on Monday morning.
“An Garda Síochána has been and continues to keep the family of Jo Jo Dullard fully updated in relation to this investigation and they have been fully apprised of all of today’s developments,” Supt Burke added.
On 9 November 1995, Ms Dullard travelled to Dublin, where she spent the evening at Bruxelles Bar on Harry Street.
That evening, she missed her last bus home to Kilkenny and, at 22:00 local time, instead boarded a bus to Naas in County Kildare, intending to hitchhike the rest of the way to Callan.
Ms Dullard caught a ride from Naas to the old N9 road near Kilcullen.At about 23:15 she got another lift to Moone.
Once in Moone, at 23:37, Ms Dullard made a phone call to her friend, Mary Cullinan.During the call she told Ms Cullinan a car had stopped to offer her a ride and she was planning to accept it.
This was the last known interaction she had with anyone she was reported missing by her sister, Kathleen, on Friday 10 November.
For 29 years Ms Dullard’s whereabouts have been the subject of a sustained police investigation.