In 1973, two nights after Christmas, the teenage daughters of Thomas Niedermayer - the 45 year old German boss of the Grundig electronics plant in Belfast - answered a knock on the door.
Two strangers asked Gabriella and Renate to fetch their father, telling the girls they had accidentally damaged his car.
Thomas Niedemayer was then attacked and bundled into a car by the Provisional IRA in front of his stunned daughters. They never saw their father again.
The abduction was the beginning of a botched kidnapping by the Provisional IRA that would ultimately result in an unprecedented tragedy even by Northern Irish standards for the three remaining members of the family who were left in the house that night.
In the days and weeks following the kidnapping, Thomas Niedermayer's wife Ingeborg and two teenage daughters waited for news. His body was eventually discovered seven years later (1980) face down at the bottom of an illegal rubbish dump.
Ten years later (1990), Ingeborg returned to Ireland (she had moved back to Germany after her husband's body had been found). Ingeborg booked into a Wicklow hotel and asked for a sea view with a double bed, as she found an empty single bed too upsetting. The following morning, her body was found on the shoreline. She had walked into the sea at Greystones and drowned. Her family says she never recovered from the murder of her husband.
Over a decade later, in January 2012, on RTÉ Radio 1's Liveline, Joe Duffy mentioned this kidnapping and the subsequent death by suicide in Greystones of Thomas Niedemayer's widow.
Subsequently, Joe received a letter about the kidnapping of Thomas Niedermayer. It said there was a lot more to this story and if he could track them down and if they agreed, he should talk to the only surviving relatives of Thomas Niedermayers - Gabrielle's two daughters - Tanya and Rachel.
Forty years on from Thomas' kidnapping, and for the first time ever, the only remaining members of the Niedermayer family - Gabrielle's two daughters Tanya and Rachel - speak publicly about what happened to the family members left behind on that night in 1973.
In 'Documentary on One - A Knock on the Door', these two sisters tell their family's story; the story of a forgotten kidnapping and how it irrevocably changed the lives of three generations of the Niedermayer family.
Narrated by Joe Duffy.
Produced by Ciaran Cassidy.
Production Supervision by Liam O'Brien and Joe Duffy.
First broadcast 16th February 2013.
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