LONDON—A French couple were jailed for life on June 26 for murdering their young nanny and burning her body in their back garden in London after months of mistreatment, threats, and physical abuse that left her a virtual prisoner.

Sabrina Kouider, 35, and Ouissem Medouni, 40, were described at the Old Bailey court as having spun a web of lies to justify the torture and murder last year of Sophie Lionnet, 21, from Troyes in eastern France.

They were told they would both have to serve at least 30 years in jail.

Lionnet’s ordeal culminated in a series of “interrogations” conducted by the duo over a 12-day period in a bid to force her to confess to various false crimes they had accused her of.

The trial heard how Kouider held a bizarre view that the nanny was working with Mark Walton, the founder of pop group Boyzone. Walton is the father of Kouider’s youngest child.

Kouider accused the nanny of helping Walton in a plot to win custody of the child and frame her and Medouni for crimes against their children.

“This was a distressing trial and must have been very upsetting for the family to hear all of the evidence of how Sophie was treated before she was eventually killed and her body burned,” said Julius Capon, head of the London Crown Prosecution Service (CPS) homicide unit.

“We are very grateful for the excellent work the Metropolitan Police did ... and also for the help the French authorities provided in ensuring the killers were brought to justice,” he added in a statement on the CPS website.

After the verdict last month, Detective Inspector Domenica Catino said, “We will never know the full extent of the horrors Sophie had to endure.”

She added in a statement, “I cannot imagine what thoughts were going through Sophie’s mind whilst being held a prisoner in those 12 days leading up to her death, but from the harrowing images obtained, it showed a scared, broken, and emaciated young girl who probably knew she was shortly facing death.”

Lionnet had first got the job after meeting Kouider’s brother in France, and initially, things appeared to go well.

However as the months went on, it became apparent to those who knew her that Lionnet had been inveigled into a uniquely bizarre and oppressive household ruled by Kouider’s violent mood swings, police said.

Other local nannies observed that Lionnet seemed to think it was normal that she was barely paid, and she dropped hints over time that she was both scared and hungry.

A fish and chip shop owner that Lionnet had visited recalled how she had grabbed food as if starving and revealed in a fearful fashion how she was beaten.

Medouni was caught when firefighters were called to the couple’s house after a neighbor became concerned about the excessive smoke coming from the bonfire at their house in Southfields, southwest London.

When confronted, Medouni claimed he was cooking sheep but the firefighters contacted police.

Medouni and Kouider had previously admitted perverting the course of justice by way of preventing a lawful burial of a body.