(ANSA) - Rome, July 18 - Silvio Berlusconi's former aide Marcello Dell'Utri is being investigated in Palermo for allegedly extorting money from the ex-premier, judicial sources said on Wednesday. The media-magnate, who is expected to run for a fourth term as premier next year, was called up by Palermo prosecutors for questioning about the case on Monday but reportedly failed to attend the meeting because of official business that presented a "legitimate impediment". Media reports had said the prosecutors wanted to question Berlusconi about alleged negotiations between the State and the Sicilian mafia in the early 1990s. Dell'Utri is set to have a retrial after receiving a seven-year jail sentence for allegedly helping the Mafia. Italy's supreme Court of Cassation in March ordered the retrial, saying Dell'Utri's legal rights had not been respected in the first appeal trial against the original conviction. But in its explanation of its decision to order a retrial, it said there was evidence that Dell'Utri had acted as an intermediary with the mafia for the ex-premier, handing on "substantial sums" of money for protection. Dell'Utri is a Senator in the ex-premier's People of Freedom party, which he is credited with helping to create in 1993 in its former form, Forza Italia.