The 21-year-old was last seen on the 9th of November 1995, after leaving a night out in Dublin to make her way home to Callan, in County Kilkenny.
The man arrested as part of the investigation into the murder of Jo Jo Dullard, has been released without charge.
Gardai are still searching land on the Kildare/Wicklow border, which may take up to a week.
The 55-year-old man was arrested on Monday – becoming the first person to be arrested in the 29-year investigation into the disappearance of Jo Jo Dullard.
He was questioned over the course of 24 hours but was released without charge this afternoon.
Gardai say searches, which started yesterday on land in Grangecon on the Kildare/Wicklow border will continue and which may take up to a week, as there is a large area to cover.
The location is about a 15 minute drive from where Jo Jo Dullard was last seen in Moone, County Kildare as she tried to hitch a lift home to Kilkenny in November 1995.
Two diggers and metal detectors were used in today’s search, while a forensic archaeologist was also on site.