An elderly Spanish doctor who became the first person to stand trial over the country’s infamous “stolen babies” scandal has been found guilty of all charges but acquitted because the statute of limitations had expired.

Eduardo Vela, who worked as a gynaecologist at the San Ramón clinic in Madrid, had been accused of taking Inés Madrigal from her biological mother in the spring of 1969 and giving her to the 46-year-old woman who was falsely certified as her birth mother and who would raise her.

Prosecutors had sought an 11-year prison sentence for Vela on charges of unlawful detention, falsifying official documents and certifying a nonexistent birth.

Judges at Madrid’s provincial court on Monday said that Vela’s landmark trial, which began at the end of June, had “indisputably proved” that he had committed the three offences and it was “crystal clear” the doctor, now 85, had faked official documents and handed the baby over to a couple who were not her parents.

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However, they ruled that too much time had passed for a conviction since Madrigal could not have been unlawfully detained once she became an adult and had only brought her complaint against Vela six years ago.

“As a consequence of all the above, and noting that the complainant reached her majority on 4 June 1987, and that the statute of limitations for the most serious crime – unlawful detention – is 10 years, and that the complaint was brought in April 2012, the crimes have expired under the statue of limitations,” they said in their judgment.

The trial was a test case for the thousands of families who are thought to have been caught up in the illegal practice, which began shortly after Franco’s victory in the civil war and continued until well after the dictator’s death in 1975.

According to some estimates, as many as 300,000 babies may have been taken from their birth mothers and placed with families who supported the Franco regime. Some of the stolen children are thought to have been placed with families in the US and Latin America.

Among those women targeted were single mothers, those with “degenerate” political views or those from poor backgrounds.

Facebook Twitter Pinterest Dr Eduardo Vela. Photograph: web

Madrigal, whose mother told her she was adopted when she turned 18, described the court’s decision as “bittersweet” and said she would appeal against it.

“I feel good because the judges acknowledged the theft, but of course I don’t agree with the statute of limitations point,” she told the Guardian.

Her lawyer, Guillermo Peña, had argued that the statute of limitations should not apply to his client’s case as she had not discovered she had in fact been stolen – rather than just adopted – until 2010.

“I didn’t know about any of that in 1987,” said Madrigal. “But Vela’s lawyer brought up the statute of limitations again and again during the trial – right from the start. And yet the Madrid provincial court has always been opposed to the statute of limitations and had previously always found in our favour.”

Madrigal said the next step would be an appeal before the supreme court.

“We’re going to keep fighting.”

Madrigal said her mother, who died two years ago at the age of 93, had supported her efforts to find justice and answers.

“I always say she didn’t give birth to me but I was born in her heart,” she said before the trial. “She lived to look after me and see me happy.”

Madrigal, a railway worker and president of the Murcia branch of the SOS Stolen Babies association, had also acknowledged that the proceedings were unlikely to bring her real closure or help her find her birth mother.

Vela, who oversaw the clinic for 20 years, told the court that he could not remember details of how it was run. A policeman who investigated the case concluded that the hospital had been used as a source of trafficked babies, and said that Vela had told him that he had burned the archive files.

Madrigal said she hoped her legal action would be first of many brought by stolen babies and their families, arguing that people like her had been torn from their parents, trafficked and ignored for too long.

She said some of the stolen children had been placed with families in countries including the US, Mexico and Chile.

“We were Europe’s baby supermarket and babies were stolen for 60 years,” she said.