Many in Spain believe the practice began as early as 1939, the year the dictator Gen. Francisco Franco came to power: newborns taken without their mothers' consent — often even without their knowledge.
In recent years, thousands of stories have surfaced depicting a startlingly similar scene. Advocates tell of a sinister web of government officials, doctors, nuns and priests, collaborating to force or deceive new mothers into letting their infants go, usually by telling them their children had died at birth — all while spiriting those infants away, to be given or sold to parents deemed wealthier or more ideologically pure.
By the estimate of at least one group, which advocates for children who say they were stolen at birth, as many as 300,000 children were taken from their mothers during a span that stretched even beyond Franco's death in 1975.
And in all that time, no one stood trial for participating in the scheme. Until now.
The trial of Eduardo Vela, 85, opened Tuesday in Madrid as protesters gathered outside, wearing yellow gloves and bearing signs calling for justice. The retired gynecologist stands accused of separating Inés Madrigal from her mother in 1969 and giving her to another woman.
If convicted of certifying the other woman as Madrigal's birth mother, Vela faces the prospect of more than a decade in prison for falsification of official documents, illegal adoption and unlawful detention.
But for many in Spain, Vela's trial is about more than the charges Vela faces and wholly denies. Rather, it's about healing — and seeking answers to difficult questions that surfaced widely only in recent years.
Two men, Juan Luis Moreno and Antonio Barroso, came forward in 2011 with the revelation that their respective fathers had purchased them when they were babies. Moreno told the BBC he learned of his own origins as his father lay on his deathbed.
"He said, 'I bought you,' " Moreno said in a 2011 documentary. "That's that's engraved here in my mind and in my heart: 'I bought you from a priest in Zaragoza.'
"And he said that Antonio had been bought, as well," Moreno added. "I asked my dad, 'How much did you pay for me?' He said 150,000 pesetas. I cost the same as a flat."
As NPR's Sylvia Poggioli reported in 2012, it was not uncommon for parents to pay the equivalent of up to $25,000 by today's standards: "The guiding principle was that the child would be better off raised by an affluent, conservative and devout Catholic family," she explained.
Madrigal, now in her late 40s, says she experienced a similar fate, except that her mother asserts Madrigal was given — not sold — to her. Before her death a few years ago, the mother told her story to CNN:
"On the day Madrigal was born, she says the head doctor at the maternity clinic, Dr. Eduardo Vela, summoned her for a 'surprise.'
"When she arrived, she says, he placed a newborn baby in her arms and handed her a falsified birth certificate. The baby was small, born premature, she says.
" 'The doctor said 'Just put her in the car between two hot water bottles,' Perez recalls. 'A woman came in with the doctor. She was wearing operating clothes and trying not to show her face. Of course, you realize all this [with] hindsight.' "
And the BBC notes that Madrigal is not the only person to cast suspicion on Vela, who had attracted police interest as early as 1981.
"Have I sold children and bought children? No," Vela told the broadcaster in the 2011 documentary, saying everything he did was in line with the laws of the time. Anything else he dismissed as "journalistic stories and nothing more."
Vela is not the first to face charges — a distinction claimed by a nun that El Pais describes as a deputy at Vela's clinic, Sister Maria Gomez, who nevertheless died not long before her trial could officially open.
Still, Vela's case holds special significance for the demonstrators who gathered Tuesday outside the court in Madrid, even if Madrigal and others hold only slim hopes of finding satisfying answers. To them, the case represents something more.
"It is a very important day for all those who are affected and for all mothers," one demonstrator, who believes her child was stolen in 1979, told Agence France-Presse. "Because a precedent is created by this man sitting in the dock."