Garda∅ are studying video footage from security cameras at Belfast port and airport in the search for missing German visitor Ms Bettina Poeschel.
Senior officers say they are still mystified by the disappearance of the 28-year-old journalist who vanished three weeks ago today.
Ms Poeschel has not been seen since September 25th after she travelled from Dublin to visit Newgrange, Co Meath.
Her father, Juergeu, and younger sister, Cornelia, are due to return to Ireland this week for their third meeting with garda∅ since the alarm was raised.
Some 40 officers are assigned full time to the investigation and the search area for Garda dog units scouring the landscape for clues has been extended.
Members of the Garda water unit have searched the river Boyne but are making repeat dives every two or three days in case fresh clues emerge.
"In addition, hundreds of statements have been taken, thousands of people have been interviewed and all the houses from Drogheda to Donore have been visited," said Chief Supt Michael Finnegan. who is leading the investigation.
Several members of Operation Trace, the specialist Garda unit set up to investigate the disappearances of six other young women in Leinster since 1993 are involved in the search, but Chief Supt Finnegan said there was no evidence to date to link her case with the earlier ones.
Ms Poeschel was in Ireland on a short break and was staying with a friend in Dublin when she set off to visit Newgrange.
The last confirmed sightings of her were between 10 a.m. and 10.30 a.m. as she left Drogheda railway station heading towards the bus station which runs a shuttle service to Newgrange, six miles away.
Garda∅ are examining photographs and camcorder footage taken by visitors to Newgrange in the hope they may have unwittingly caught the missing woman on film.
The examination of footage from Belfast is to rule out the possibility that she left the State via the North.