The lover of a wealthy French financier yesterday admitted that she shot him four times while he was bound to a chair dressed in a latex body-suit.

Cécile Brossard, 40, interrupted a murder trial in Geneva to say that she wanted to ask for the "forgiveness" of the family of Edouard Stern, but she knew that, "there could be no forgiveness for such an abominable act".

M. Stern, 50, one of France's most influential men and a friend of President Nicolas Sarkozy, was murdered in his apartment in Geneva in February 2005. He and Mme Brossard, a call-girl turned artist, had a tempestuous, four-year sado-masochistic love affair before they quarrelled over her demands for $1m (£660,000) as a "token of his love".

Download the new Independent Premium app Sharing the full story, not just the headlines

After a series of disputes and reconciliations, in which M. Stern first paid, and then blocked, the money, Mme Brossard admits going to his apartment and shooting him during an elaborate sexual game. She claims that the killing was a "crime of passion", provoked when the tied-up banker said: "A million dollars is a lot of money to pay for a whore."

In an unscheduled opening statement on the first day of a nine-day trial yesterday, Mme Brossard spoke warmly of the man she had murdered: "He was an intelligent man, a refined man, an extraordinary man in every way.

"I don't want this trial to tarnish his memory. I just want to explain what brought me to that point."

Earlier the court heard statements in camera from M. Stern's three children, aged 18 to 24, and from his estranged wife, Béatrice. She described him as an "extremely nice man ... with faults, who could be very demanding of himself and those whom he loved."

Suspicion for M. Stern's murder initially fell on the Russian mafia after it emerged that he had been involved in troubled business dealings in Moscow. Several books and a movie have been devoted, directly or indirectly, to his double life and bizarre death.

From the age of 24, when he took over the family bank, ejecting his father, M. Stern had had a brilliant and controversial career in high finance. He married Béatrice David-Weill, the daughter of the owner of the powerful bank Lazard. In 1997, he split acrimoniously with his father-in-law and started his own investment company, which conducted a series of high-profile deals.

The basic facts of his murder are not in dispute. During his relationship with Mme Brossard, they both tried to dominate the other. When she came to his Geneva apartment on 28 February, they quarrelled over the blocked payment and then made up.

Daily coronavirus briefing No hype, just the advice and analysis you need Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive morning headlines Monday - Friday plus breaking news alerts by email Update newsletter preferences

In her confession statement to police, she said that the banker got into his flesh-coloured body-suit and asked to be tied to a chair and whipped. She put on her black boots and fishnet stockings. "We were completely wrapped up in our game," she told police. "Then, looking straight at me, he said: 'A million dollars is a lot to pay for a whore.' Something snapped inside me."

She said that she went to his dressing table, chose one of the three revolvers there and shot him first twice in the head and then twice in the body.

Her lawyers claim that she was – and still is – sincerely in love with M. Stern, and was driven to distraction by his often repeated, and then withdrawn, offers of marriage and money. If they can convince the jury that she committed a "crime of passion" she would face a jail sentence of no more than 10 years, four of which she has already served.

Her principal lawyer, Maître Alec Reymond, said yesterday that she had spent 12 sessions in a psychiatric clinic since her arrest and confession.

He said that Mme Brossard believed that she was still "in contact" with her murdered lover and that they were "united for eternity".

The lawyer representing M. Stern's family, Maître Marc Bonnant, will argue that she committed an unpremeditated but financially motivated murder and should be given a 20-year sentence.

He said yesterday that a "crime of passion" implied that "the victim was not innocent and played a role in his own murder".

"The circumstances were sexual, but not the cause of his death," he said. "This was not a sexual act gone wrong. It was murder committed during a sexual act but not a sexual crime."

The Stern family lawyer will also point to the fact that Mme Brossard fled to Australia and came back again just after the murder as evidence of a "calculated" attempt to cover up her crime.