Investigators have seized a book that the model was writing and are seeking to determine the exact cause of her death.
They have interviewed Ms Fidal’s brother, who reportedly said she was convinced she had been poisoned.
Prosecutors were only told of her death a week ago, a week after she passed away.
Ms Fidal was one of three young women who claimed that Mr Berlusconi’s “bunga bunga” gatherings, held at his villa outside Milan, were sordid sex parties.
Their testimony is at odds with around 25 other starlets, who claimed the parties were “elegant dinners”.
Prosecutors claimed they were paid to lie under oath by Mr Berlusconi, the billionaire businessman.
Mr Berlusconi, who still plays an active part in politics and remains head of the centre-Right Forza Italia party, was accused of paying for sex with an underage escort girl who called herself “Ruby the Heart Stealer”.
He was initially convicted of the charge and sentenced to seven years in prison, but then acquitted on appeal, after judges accepted his argument that he did not know the young woman was under the age of 18.
Ms Fadil expressed her incredulity at the time of his acquittal in 2014.
"From seven years to zero – how is that possible?" she told La Repubblica newspaper.
“In Milan, in certain circles, it was often discussed that by going to bed with the prime minister one could earn money."
She said women performed stripteases at the parties dressed as nuns, nurses and police officers.
Mr Berlusconi described the parties as "burlesque contests" and "theatrical spectaculars".
Since then he has been embroiled in allegations that he paid the young women a total of around 10 million euros to keep quiet about what really went on.
The hedonistic soirees were dubbed "bunga bunga" parties after a politically incorrect joke told by Mr Berlusconi about European explorers encountering an African tribe of cannibals.
The 82-year-old has announced his intention to run in the European Parliament elections in May, in what would be yet another comeback from sex scandals, court cases and allegations of financial impropriety.
His party performed poorly in a general election last March and was comprehensively eclipsed by The League, run by Matteo Salvini, who is now interior minister in a coalition with the Five Star Movement.
A model who was caught up in the scandal of Silvio Berlusconi’s notorious “bunga bunga” parties has died, allegedly of poisoning.
Moroccan-born Imane Fidal was a key witness in a trial in which the former prime minister is accused of bribing actresses, models and escorts to lie in court about the alleged sex parties.
Italian judicial authorities have opened a murder investigation into the death, the details of which are murky.
Ms Fidal, 34, died two weeks ago in a hospital in Milan from chronic organ failure but the story only emerged on Friday.
She had reportedly been complaining of chronic stomach pains and told friends and family that she believed she had been poisoned, according to Francesco Greco, a prosecutor in the case.