Three years ago, the sleazy world of Via Lulli in Milan is alleged to have entered into bloody and sensational collision with the prosperous area of Corso Vittorio Emanuele.

At a trial due to start later this month, it will be claimed that on March 27th, 1995, two men hired by a night porter, Ivano Savioni, were waiting for Patrizia Gucci's husband Maurizio when he turned up at his office, also in the centre of Milan. One followed him into the building and shot him dead while the other waited outside in a getaway car.

High-life and low-life Milan are still in surreal juxtaposition as a result of that murder. Among those arrested and charged with a role in it was Patrizia Gucci. For the last two years, she has been living in surroundings that could scarcely be more different from those to which she is accustomed

in a cell painted institutional green and plastered with photos of actors and chocolate-box top landscapes ripped from magazines by one of her cellmates.

When local politicians visited the San Vittore prison last year, they found Patrizia Gucci swathed in heavy woollens, complaining of the cold, but still wearing four-inch heels and lamenting prison rules forbidding her access to cosmetics. "I cannot get by without my make-up," she told them.

Maurizio Gucci's death was a sadly appropriate end for the last member of a family as famous for its savage internal disputes as for its impeccably designed and crafted leatherware. The intertwined Gs of its famous brandmark were the initials of the firm's founder, Guccio Gucci, a Florentine who ran away to England as a boy and became a waiter at the Savoy hotel. There, he was able to observe the rich at close quarters and develop an appreciation of their tastes. Back in Florence, he set about making those leather goods with the hint of horsiness that would attract, above all, the newly wealthy and the socially aspiring.

Gucci recognised that the biggest danger to any successful family business was the risk that succeeding generations would lack the guile and skill of its founder. He set about systematically pitting his children against one another, a tradition of internal conflict that would lead one of the Guccis to report his own father for tax evasion and have him jailed when he was in his eighties.

When Maurizio Gucci took over as chairman in 1983, his relationship with his uncle, who had been ousted, was so bad he had the locks on the older man's office changed. His uncle did not, in the event, try to return by force. He had Maurizio prosecuted for fraud instead.

Maurizio's empire ended in failure. Ten years after he took over, the firm passed out of family control and into the hands of a Bahrain-based merchant bank.

A change in his personality will be at the core of the trial due to begin this month, for it appears to have been at the origin of the split with his wife.

Patrizia Gucci had been one of Milan's outstanding beauties, often compared with Elizabeth Taylor. She was equally renowned for her love of wealth and luxury, and a character that was at once capricious and steely.

It has emerged since her arrest that she wrote a book about her marriage after it broke down. In the unpublished manuscript, she reconstructs a row she had with Maurizio soon after he took over as Gucci's chairman.

She has him saying: "For too long I have been under the heel of my father and, let us be frank, your control. All too often, the two of you have joined forces to make me do your will. All too often, I have felt like a puppet yet kept quite."

"Where had her Maurizio gone?" the narrator asks. "These were the words of a profoundly changed man."

The prosecution's case will be that Patrizia could not cope with the breakdown of her marriage, with the reality that she was no longer Empress of the House of Gucci and that, obsessed with revenge, she set out to get her husband murdered. The key evidence will come from one Giuseppina Auriemma.

It is she who provides the link between Via Lulli and the penthouse off Corso Vittorio Emanuele. Born 52 years ago in the same village near Naples as Ivano Savioni, the erstwhile night porter at the New Milan hotel, she was Patrizia Gucci's best friend.

Not any longer, though.

Two months ago, Auriemma signed a confession in which she admitted getting Ivano Savioni to recruit the killers of Maurizio. She added that since she and Patrizia were jailed, her friend had tried to bribe her to take full responsibility.

She told prosecutors that "in exchange, she would have granted me a gilded imprisonment and, whenever I came out, two billion lire (£760,322)". Auriemma met the Guccis 20 years earlier while they were holidaying on the southern island of Ischia. She later ran a Gucci boutique in Naples, but the business failed and thereafter, says her lawyer, Pietro Traini, she was kept by her family.

When Auriemma was arrested she was described to the media as a maga, a word that means "sorcerer" but is also often used to describe fortune-tellers. Both Traini and Patrizia's counsel, however, deny there is any occult dimension to the case. "Patrizia Gucci is fascinated by that sort of thing," Traini says. "Ms Auriemma used to go along with her to see fortune-tellers. That is all."

The exact nature of the relationship between the two is crucial to the outcome of what promises to be an absorbing case. Traini describes his client as "La Gucci's succubus", a description scarcely calculated to curb speculation about esoteric undertones. Patrizia's counsel, Giovanni Dedola, maintains that, on the contrary, it was his client who fell under the malign spell of Auriemma.

A report drawn up for Patrizia's lawyers by medical experts noted that she showed a "peculiar indifference towards her murdered spouse and her own situation as someone facing trial for the crime". They regarded this as symptomatic of a lack of critical faculty linked to her operation for brain cancer six years ago. "After the operation, she lost her judgment," Dedola claims. "That is when La Auriemma began to exert a special influence."

He admits his client was obsessed with the idea of her husband's death, but says that she never had any serious intention it should happen. The result, however, was that she walked into a trap of diabolical ingenuity, hatched by a woman who had secretly begun to detest her.

"The psychological twist to this tale is that La Auriemma saw Patrizia as the person she wanted to be and could not be," Dedola says. He claims she borrowed 150 million lire from her friend, saying she needed the money to pay debts but instead gave it to the killers as a down payment. Her aim was to blackmail Patrizia with evidence pointing to her guilt once her estranged husband had been murdered. "My client," he says, "was first swindled, then blackmailed."

How the jury will react to this twisted mass of evidence is anybody's guess. The only certainty is that, with the trial expected to last for at least a year, the question of who killed the last of the great Gucci family will preoccupy Italians for a long time to come.