A French couple have been found guilty of murdering their 21-year-old au-pair, whose burnt body was found in their London garden in September last year.

Sabrina Kouider, 35, and her partner Ouissem Medouni, 40, were found guilty by a jury at London's Old Bailey court of murdering French live-in nanny Sophie Lionnet and burning her body on a garden bonfire.

"Only Kouider and Medouni know exactly how they killed Sophie but the prosecution was able to prove that she died as a result of purposeful and sustained violence, and not by accident," said Aisling Hosein from the Crown Prosecution Service.

"They were both jointly involved and came up with a plan to try and destroy her body and escape responsibility for this horrendous crime for which they have been found guilty," she added.

The jurors deliberated for a week before unanimously convicting Kouider and ruling by a majority decision of ten to two that her partner Medouni was guilty.

Kouider is to undergo psychiatric assessment before sentencing, which is due to take place on 26 June.

Both denied murdering Lionnet, although they had admitted burning her body in their garden.

The court heard how the couple had interrogated and tortured Lionnet over their belief she was conspiring with one of Kouider's former boyfriends - Mark Walton, a former member of Boyzone.

The court heard how fashion designer Kouider was fixated with Mr Walton.

After splitting up after two years, Kouider reported him to police more than 30 times and received a caution for branding him a paedophile on a fake Facebook profile.

Giving evidence, LA-based Mr Walton said he had been "in love" with Kouider but she would "flip" and go "crazy" for no reason.

Kouider told London's Old Bailey court that she hit the au pair "really bad" with an electrical cable.

Both she and Medouni accused each other of killing her.

In her testimony, Kouider said her partner - who she called "Sam" - was violent to her and "was with me for sex, nothing else, and money".

Their lawyers have 30 days to appeal the decision.

Ms Lionnet's mother Mrs Devallonne described her daughter's killers as "monsters".

She said: "These self-obsessed individuals who murdered Sophie did not believe Sophie had a value.

"These monsters repeatedly beat Sophie. 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 victim's father Patrick Lionnet said: "Sabrina and Ouissem have not only stolen the life of my daughter so brutally and without remorse, they have also stolen mine."

He said what the couple did to his shy and reserved daughter was "beyond comprehension" and "unforgivable".

Sophie Lionnet's parents pictured outside the court

Ms Lionnet was born in Troyes, in northern France, and completed a vocational childcare course before the opportunity to work as a nanny in London arose.

At first she seemed "happy" and things were "fine" in her first job with Kouider and Medouni, jurors heard.

In the six months before her death, Ms Lionnet seemed "fed up" and wanted to go back to her family, according to her mother.

In a revealing letter to her mother in June last year, Ms Lionnet admitted she was a "stupid idiot" who was "fooled" by words.

In a final call on 8 August, Mrs Devallonne recalled her daughter was crying on the phone and seemed "a bit disoriented".

By then, her employers had stopped paying her £50 a week wages, beat her, interrogated her, and accused her of stealing a diamond pendant.

This photo of Sophie Lionnet was taken two days before her body was found

Prosecutor Richard Horwell QC told jurors that neither were prepared to admit the truth - that they killed Ms Lionnet out of "revenge and punishment".

He said their "unhealthy, myopic, all-consuming and groundless" obsession with Mr Walton had deprived them of reason and turned their nanny into "something less than human".

Additional Reporting PA