Pop star’s ex-girlfriend and her boyfriend convicted of murdering, burning au pair in garden

The ex-girlfriend of a former boy band star and her boyfriend were found guilty Thursday of murdering their French au pair and burning her body on a bonfire as they barbecued chicken.

Sabrina Kouider, 35, and Ouissem Medouni, 40, were convicted by a jury at the Central Criminal Court of killing au pair Sophie Lionnet, 21.

au pair

Sophie Lionnet was found dead on Sept. 20, 2017.  (Metropolitan Police Service)

The French couple, who had a turbulent on-off relationship, denied killing Lionnet, though they admitted to disposing of the body. Each blamed the other for the death

Lionnet’s body was found at a home in southwest London on Sept. 20, 2017.

Mark Walton_VTV

Mark Walton said he dated Sabrina Kouider for two years.  (VTV )

Prosecutors said the pair killed Lionnet after becoming obsessed with the belief she was conspiring with Kouider’s ex-boyfriend Mark Walton, a founding member of Irish boy band Boyzone.

Kouider was said to be fixated on Walton and believed Lionnet was having an affair with him and helping him carry out a sex-abuse plot — though in fact the two had never met. Kouider and Medouni, a banker, repeatedly beat and interrogated Lionnet in an attempt to make her confess.

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backyard

Sabrina Kouider, 35, and Ouissem Medouni, 40, barbecued chicken nearby as Sophie Lionnet was burning.  (London's Metropolitan Police)

Prosecutors claimed the couple starved Lionnet, beat her with an electrical cable and tortured her by dunking her head underwater. After killing her in a bathtub in September, they threw her body on a bonfire in their yard in an affluent area of southwest London near the home of the Wimbledon tennis tournament as they barbecued chicken nearby.

bathroom

Prosecutors claimed the couple starved Sophie Lionnet, beat her with an electrical cable and tortured her by dunking her head underwater in the bathtub.  (London's Metropolitan Police)

When neighbors called firefighters because of the pungent-smelling smoke, Medouni claimed the charred remains belonged to a sheep.

Walton, who’s now a music producer in Los Angeles, said his two-year relationship with Kouider was “the most turbulent relationship I had ever been in.”

He described in court how she would sometimes "flip, get very angry, very loud and just not care where we were. She would just go crazy over something trivial."

He continued to pay Kouider's rent for a time after they split up in 2013. After he stopped, she began a campaign of harassment, reporting him to police more than 30 times for allegedly sexually abusing a cat, using black magic and hiring a helicopter to spy on her. Frustrated that police were not taking her seriously, she accused Walton on Facebook of being a pedophile.

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Prosecutor Richard Horwell told jurors that the couple's "unhealthy, myopic, all-consuming and groundless" obsession with Walton had deprived them of reason.

The pair is slated to be sentenced on June 26.

The victim's mother, Catherine Devallone, wept in court, and called her daughter's killers "monsters."

"These monsters repeatedly beat Sophie," she said in a statement. "They starved, tortured and broke her. They took away her dignity and finally her life.

"Our Sophie will soon be laid to rest. No god will ever forgive you both for what you have done to our daughter."

The Associated Press contributed to this report.