It was one of the darkest episodes of the Troubles – the German industrialist Thomas Niedermayer abducted, murdered and secretly buried by the IRA – and nearly 40 years on, the full story of its far-reaching effects has finally been told.
The catastrophic chain of events set in motion on the night he was bundled into the boot of a car in west Belfast had until now been almost forgotten.
But in a powerfully emotional documentary broadcast on RTE radio on Saturday, Niedermayer's grandchildren told their family's tragic story.
In A Knock on the Door, presenter Joe Duffy pieced together what happened the Niedermayers after that fateful night in Christmas week 1973 when two teenage girls, Gabrielle and Renate, innocently opened the door to their father's kidnappers. The men at the door asked them to fetch Thomas, claiming they'd accidentally damaged his car. The girls watched helplessly as their father was dragged away.
TV and radio appeals of their mother, Ingeborg, were replayed in her broken English begging the IRA for information.
Thomas was already dead and buried in a rubbish tip in west Belfast but the IRA remained silent. His body wasn't discovered for seven years.
In 1990, Ingeborg returned to Ireland. She booked into a Co Wicklow hotel, asking for a room with a sea view. A double room, she told staff, because although her husband was dead, she couldn't bear a single bed.
She later went to an isolated beach and walked into the sea. She had been in hospital on the night Thomas was kidnapped and always believed that had she been at home, she could have prevented his abduction.
Thomas' daughters were also haunted by the unwitting role they'd played by opening the door. Renate killed herself a few years later. In 1994, Gabrielle also took her own life. In just over two decades since the abduction, every member of his family present that night was dead.
Gabrielle's daughters, Rachel and Tanya, pieced together their story through bundles of newspaper clippings their mother had kept about their grandfather's abduction for the show.
"She wanted to be the best mother she could. She loved us with all her heart. But she had lost her whole family. She was the sole survivor. She was very depressed," Rachel recounted.
On the show, the sisters heard for the first time recordings of their mother's heart-rending appeals in 1974 to the IRA for information about her father.
Thomas had been guilty of no 'crime' even by republican standards. His Grundig factory was one of the few in Northern Ireland not to practise religious discrimination.
The Provos' 'plan' had been to trade him with the British for the repatriation of the Price sisters, Marian and Dolours, from England, where they were being held on bombing charges.
Thomas died when one of his abductors battered him with a gun as he tried to escape.
What happened to the businessman's family, as Joe Duffy said, there was no end to this story: "It reverberates through the generations."
Most importantly, it was a reminder of the devastating ripple effect of violence and the unseen price it can inflict on those who have done no wrong.