Kouider and Medouni were found guilty of murder on Thursday, May 24, after a week's deliberation by the jury at the Old Bailey in London.
When Sophie Lionnet agreed to take a job with her compatriots in London she had no idea that she was signing her own death warrant.
The 21-year-old was from Troyes, a city in central France which can trace its history back to the Roman Empire.
Sophie's mother Catherine and grandfather Stephane Devalonne were in court when prosecutor Richard Horwell QC described her as an "ingénue."
She had been introduced to the couple by Kouider's brother and, after a successful work trial in 2015, she returned to London in January 2016 to take up employment.
In September 2017 police arrested Medouni and Kouider as they burnt Sophie's body on a bonfire in their back garden.
But what happened in the intervening months to explain such a horrific event?
'Cut Throat' Defense
The trial at the Old Bailey in London saw a classic "cut throat" defense with both blaming the other for the crime, which revolved around an obsession Kouider had about her ex-boyfriend, Mark Walton, one of the founders of the phenomenally popular Irish boy band Boyzone.
Catherine Devallonne, mother of murdered nanny arriving at the Old Bailey this morning pic.twitter.com/OiTZjx77eh— CourtNewsUK (@CourtNewsUK) 24 May 2018
"Walton is a wealthy man — and good luck to him for that — but it is of course a truth universally acknowledged that a single man in possession of a good fortune will often be parted from it," said Mr. Horwell, who said allegations against Walton began after the Pop Idol Vietnam judge got tired of Kouider's constant demands for money.
The jury heard audio recordings Kouider and Medouni had made, during which they repeatedly interrogated Sophie about her supposed dealings with Walton, who would give evidence himself that he had never even met Sophie.
Mr. Horwell had no doubts both were jointly responsible, as he made clear in his closing speech on Friday, May 11.
"The defendants made a truly odd couple. There is a unique bond between them that has kept them together on and off for many years, a bond based partly in love and something close to it," Mr. Horwell told the jury.
"But as far as this trial is concerned the point that really matters is that together they were a truly toxic combination," he said.
Kouider was beautiful and exotic — although her charms had faded somewhat after spending almost a year in custody — and claimed to have been friends with Donald Trump and celebrities like singer Duncan James from British boy band Blue.
But she had a fearful temper, craved attention and was wildly promiscuous.
Sabrina Kouider, who had ranted at her former lover throughout the trial, wept and shook her head in the dock as the jury filed into court.— CourtNewsUK (@CourtNewsUK) 24 May 2018
As the verdicts were announced she hysterically sobbed 'no, no, no.' Medouni stared at the floor
Medouni met her in 2001 when she was just 19 and he fell in love.
Giving evidence, he said she was "very, very beautiful" and when he kissed her he felt as if he had won the Euromillions lottery.
It was a passion which would ruin his life.
Only months after they met she cheated on him with another man.
"That was my first time of falling in love (and when she told me) I felt like the world fell apart. I was very unhappy," Medouni told the court.
But they would have an on and off relationship for the next 17 years, despite her repeated infidelity and rages.
In June 2007 they went on holiday together to Greece but as soon as they got back to London she returned to Paris and when she eventually returned two months later she was pregnant by another man.
Medouni had a degree in economics and got a good job working for the huge French bank Société Générale in London. He also built up a portfolio of properties in his native Paris, which he rented out.
Kouider dabbled in fashion design but largely she made her way through life by entrapping wealthy men and getting them to pay for her lifestyle in rented apartments in fashionable districts of London.
In the witness box Medouni struck a pathetic image, a broken, softly-spoken man so downtrodden and lacking in self-respect.
He obeyed her every step along the way….until, faced with a life sentence, he finally rebelled against her.
Medouni claimed he fell asleep on the night of Sophie's death and when he woke up Kouider told him Sophie was unconscious in the bath. She was in fact dead.
He claimed she told him she had ducked her head under the water, in an attempt to make her confess, and had accidentally drowned her.
Kouider burst into loud crying and shook her head as the jury returned the unanimous guilty verdict.— CourtNewsUK (@CourtNewsUK) 24 May 2018
She began to speak, saying 'I want to-' before the judge told her to 'sit down please.'
Medouni claimed he agreed to dispose of the body and attempt to cover up for Kouider.
When Kouider gave her version of events — claiming he was responsible — Medouni interrupted her.
Outburst in the Courtroom
"You put her head under the water," he shouted across the court.
"She's a very strong woman, she can do that," he said to the jurors, before the judge, Mr Justice Nicholas Hilliard QC, called him to order.
But Kouider claimed it was he who killed Sophie.
The cut-throat defense made for lively cross examination.
When Kouider was giving evidence she claimed Medouni had tried to have sex with her only hours after Sophie was killed, with her body lying on a bed in the house.
Medouni's lawyer, Orlando Pownall QC, claimed she was lying.
"I suggest it is a figment if your imagination," he told her.
"It's not my imagination, it's the truth," she replied angrily.
Kouider, who was brought to court every day from a secure mental health unit, told the jury she remained convinced Sophie had betrayed her to Walton, for money and the chance of "fame".
But the jury concluded she was a deluded murderess and Medouni was equally culpable.
It is now up to the judge how long they should spend in prison but both face a mandatory life sentence.
She is expected to undergo a mental health assessment before they are sentenced on June 26.