A London-based fashion designer and her boyfriend were convicted of torturing and murdering their nanny, because the former believed the French woman has conspired with her ex-boyfriend, the founder of Boyzone, Mark Walton, and planned to drug and molest her family.

Sabrina Kouider, 35, and her boyfriend, Ouissem Medouni, 40, starved, beat and tortured Sophie Lionnet, 21, including dunking her head in the water, in order to coax her into falsely confessing that she was colluding with Walton, which they proceeded to record on camera before killing her, the Guardian reported. 

They then burned her body in their garden outside their Wimbledon home in south west London, as they barbecued chicken nearby. They even tried to explain her corpse as that of sheep when the neighbors alerted the fire department.

Kouider was the mastermind behind the murder plot as she was the one who had an unhealthy obsession with Walton for the past five years. Medouni, however, came to share her delusions and became an accomplice to the crime.

Due to her obsession, Kouider brought bizarre allegations against Walton, over the years. She reported him to the police 30 times with claims like using black magic, trying to sexually abuse a cat and hiring a helicopter to spy on her. She even went on Facebook and accused him of being a pedophile.

Walton, on the other hand, treated her with nothing but “integrity and honesty,” the prosecution said. He even flew over from Los Angeles, where he currently lives, to provide evidence in the baseless cases.

In a statement given to the police, another of Kouider's ex-boyfriends, Anthony Francois, described her former lover as a “fickle” and “lunatic.”

“She could be as lovable as she could be detestable,” he said, Mail Online reported. “There was no explanation for this change in her moods, she would often shout and become aggressive. Her behavior was difficult, incomprehensible.”

“She would lie, her behavior was strange, she was aggressive; sometimes she was violent and pulled the hair of girls on the street just because of a look. She took advantage of persons who were weaker than her. She had a dual face, a dual personality. She was manipulative, she could charm and tell lies,” he added.

Murder Trial Catherine Devallonne (C), the mother of murdered French au-pair Sophie Lionnet, reacts as she arrives at London's Central Crimnal Court in central London, May 24, 2018. Photo: Getty Images/ DANIEL LEAL-OLIVAS

Kouider, who was born in Algeria and grew up in Paris, had an on-and-off relationship with Medouni for 17 years, after meeting him at a fun fair at the age of 18. In between, she dated a number of men, before going back to Medouni after breaking up with Walton. 

Although she and Medouni had an Islamic marriage certificate, she would often refer him as a friend or relative in public in order to keep their relationship a secret.

When the jury announced a guilty verdict, Kouider broke down in tears and Medouni hung his head. They will be sentenced on June 26.

Lionnet’s mother Catherine Devallone claimed her daughter had never met Walton — a claim that was substantiated by the Boyzone founder himself. After the couple was convicted, she told The Sun: “I’d like the death penalty. I’d have them burned at the stake like Joan of Arc. Alive. That’s what they deserve. It’s maybe cruel but what they did was even more cruel.”