Gardaí and the PSNI are searching for three men whom they believe broke into a businessman's house in Donegal, threatened his wife and children at gunpoint and got away with a sum of money - estimated to be around €15,000.
Gardaí arrested a fourth man in connection with the armed robbery. He is now being questioned at Buncrana Garda Station.
The businessman runs his business in Derry and was not in the house at the time.
His family were traumatised but otherwise unhurt. No shots were fired during the raid.
At around 9am a gang of armed men, believed to from Northern Ireland, entered the businessman's home in Kinnego near Buncrana, Co Donegal.
Three of the men forced their way in, threatened the man's wife and four children and drove away with a sum of money in the family car - a dark blue Audi A6 registration number 09 DL 2621.
They drove towards Brigend, abandoned the car in Derry, hijacked a breadvan and then hijacked another car before escaping.
Gardaí arrested a man in his 30s, from Northern Ireland, near the house in a Silver Nissan Northern registered Almera - CZJ 2195.
Gardaí are appealing for anyone with any information or who saw the two cars today to contact them at the incident room at Buncrana Garda Station on 074-9320540, or the Garda Confidential Telephone Line on 1800-666111.