How many? More than 900 cases are being investigated, but new cases are still coming to light - lawyers say the total could reach 300,000
How long? Over a period of 40-50 years, beginning under Franco, up to the 1990s
Who benefited? Initially the Fascists by bringing up the children of their enemies - later children were taken from parents judged to be morally or economically deficient and placed with approved Catholic, often childless, families
Why did it take so long to expose? The Church and medical profession are highly respected, and Spanish law does not require the biological mother’s name on the birth certificate
In 1971 Manoli, who was 23 at the time and not long married, gave birth to what she was told was a healthy baby boy, but he was immediately taken away for what were called routine tests.
Nine interminable hours passed. “Then, a nun, who was also a nurse, coldly informed me that my baby had died,” she says.
They would not let her have her son’s body, nor would they tell her when the funeral would be.
Did she not think to question the hospital staff?
"Doctors, nuns?" she says, almost in horror. "I couldn’t accuse them of lying. This was Franco’s Spain. A dictatorship. Even now we Spaniards tend not to question authority."
The scale of the baby trafficking was unknown until this year, when two men - Antonio Barroso and Juan Luis Moreno, childhood friends from a seaside town near Barcelona - discovered that they had been bought from a nun. Their parents weren’t their real parents, and their life had been built on a lie.
Juan Luis Moreno discovered the truth when the man he had been brought to call “father” was on his deathbed.
Antonio Barroso and Juan Luis Moreno took their story to the papers - and opened the floodgates
"He said, ‘I bought you from a priest in Zaragoza’. He said that Antonio had been bought as well."
The pair were hurt and angry. They say they felt like two dogs that had been bought at a pet shop. An adoption lawyer they turned to for advice said he came across cases like theirs all the time.
The pair went to the press and suddenly the story was everywhere. Mothers began to come forward across Spain with disturbingly similar stories.
After months of requests from the BBC, the Spanish government finally put forward Angel Nunez from the justice ministry to talk to me about Spain’s stolen children.
Asked if babies were stolen, Mr Nunez replied: “Without a doubt”.
"How many?" I asked.
"I don’t dare to come up with figures," he answered carefully. "But from the volume of official investigations I dare to say there were many."
Lawyers believe that up to 300,000 babies were taken.
The practice of removing children from parents deemed “undesirable” and placing them with “approved” families, began in the 1930s under the dictator General Francisco Franco.
At that time, the motivation may have been ideological. But years later, it seemed to change - babies began to be taken from parents considered morally - or economically - deficient. It became a money-spinner, too.
The scandal is closely linked to the Catholic Church, which under Franco assumed a prominent role in Spain’s social services including hospitals, schools and children’s homes.
Nuns and priests compiled waiting lists of would-be adoptive parents, while doctors were said to have lied to mothers about the fate of their children.
The name of one doctor, Dr Eduardo Vela, has come up in a number of victim investigations.
In 1981, Civil Registry sources indicate that 70% of births at Dr Vela’s San Ramon clinic in Madrid were registered as “mother unknown”.
This was legal under Spanish law, and was meant to protect the anonymity of unmarried mothers. It is alleged that this was also widely used to cover up baby theft and trafficking.
Dr Vela stands accused of telling women their babies had died when they had not and handing over those newborn children to other couples for cash.
A Spanish magazine published photographs of a dead baby kept in a freezer at the San Ramon clinic, supposedly to show mothers that their child had died.
He refused to give the BBC an interview. But, by coincidence, I had recently given birth at a clinic he founded, so I was able to book an appointment with him.
We met at his private practice in his home in Madrid. The man painted as a monster in the Spanish media was old and smiley, but his smile soon disappeared when I confessed to being a journalist.
Dr Vela grabbed a metal crucifix which had been standing on his desk. He moved towards me brandishing it in my face. “Do you know what this is, Katya?” he said. “I have always acted in his name. Always for the good of the children and to protect the mothers. Enough.”
Dr Vela insists he always acted within the law.
After Franco’s death in 1975, the major political parties agreed an amnesty to help smooth the transition to democracy.
This World: Spain’s Stolen Babies, BBC Two, 9pm, Tuesday 18 October
Assignment, BBC World Service Radio, 3rd November
But this amnesty law has never been repealed, so attempts to investigate Spain’s baby trafficking as a national crime against humanity have been rejected by the country’s judiciary and resisted by its politicians.
"Thirty-five years have passed since the death of the dictator… Evidently, we still have problems from the past. Social problems and personal or even cultural problems and the policy of this government has been trying to solve them," says the justice ministry’s Angel Nunez.
The Spanish government’s refusal to set up a national inquiry into the scandal has frustrated affected families, who in many cases are carrying out their own investigations, as best they can.
Babies’ graves have been dug up across the country for DNA-testing. Some have revealed nothing but a pile of stones, while others have contained adult remains.
Spaniards have flocked to clinics to take DNA tests in the hope of reuniting their families.
The first few matches have now been made between so-called stolen children and their biological mothers. But there could potentially have already been so many more. Data protection laws prohibit DNA banks from sharing or cross-referencing data and the Spanish government has yet to fulfil its promise to set up a national DNA database.
Manoli Pagador is still tortured by the events of 40 years ago. She told me she has been taking medication ever since.
"You can’t just say to yourself, I have to forget it and that’s it.
"It’s not something you forget, it’s with you for the rest of your life."
Katya Adler investigates in This World: Spain’s Stolen Babies on BBC Two at 2100BST on Tuesday 18 October and on Assignment on BBC World Service Radio on 3rd November. Watch (UK only) or listen online afterwards at the above links.