A mistress who murdered a billionaire banker during a bondage session was jailed for 8½ years yesterday after a Swiss jury accepted that he had humiliated and harassed her.

Cécile Brossard, 40, nodded her thanks to the jury as she was led away to serve what could be less than 18 months in prison; she has already been detained for four years since the killing in February 2005 of Edouard Stern. She could even be given day release later this year.

The jury also ordered the destruction of sex toys and the latex rubber suit that Mr Stern, France’s 38th richest person, was wearing when Brossard put a bullet between his eyes as they argued during a sex game in his Geneva flat.

Also to be destroyed are compromising photographs gathered during the investigation into a killing that exposed Mr Stern’s taste for organising sex parties with Brossard and friends from the Franco-Swiss elite.

The speedy trial and a decision to drop initial premeditated murder charges were seen in Switzerland as an attempt to minimise publicity over a scandal that shook the high French financial establishment.

The latex suit and mask worn by Mr Stern was particularly troubling. Daniel Zappelli, the prosecutor, asked for at least an 11-year sentence, saying that Brossard showed cruelty by failing to remove the suit from his body before leaving his flat. That would at least have saved his reputation, he said.

According to media reports, Swiss judicial investigators suspected in 2005 that French government agents had taken a close interest in the case and had removed material from Brossard’s home in Paris before police searched it.

The jury convicted Brossard of unpremeditated murder yesterday, rejecting her argument that her act qualified as the lesser offence of a crime of passion. “Her cynical, deliberate and manipulative behaviour was not the one of a reasonable woman who commits a crime under an excusable emotion or despair,” the jury said. She faced a maximum 20 years in prison.

The jury, which included the presiding judge, softened its line yesterday and responded to an appeal from Brossard’s lawyer for a compassionate sentence. It called her crime particularly cowardly because Mr Stern, who was 50, had been tied up and unable to defend himself when she aimed his pistol at his head. But it acknowledged the “tumultuous” nature of the relationship and noted Mr Stern’s “humiliating, harassing and occasionally cruel” behaviour toward her.

Brossard and her lawyers had depicted Mr Stern, whose friends included President Sarkozy and other powerful politicians, as playing a vicious game with his mentally fragile and emotionally dependent mistress. She claimed to have lost her mind when, during a sadomasochistic sex session, he taunted her over a big loan he had given her, saying: “One million dollars is a lot of money to pay for a whore.”

The jury said that it had taken account of the “profound regret” that Brossard expressed during the trial and it also recognised her “slightly reduced responsibility”. A psychiatrist had testified that Brossard had a borderline personality and suffered sexual abuse as a child.

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