The suspected arson attack on Thursday came as a second woman, Patrizia D'Addario, a former model and escort who claims she spent a night with Mr Berlusconi at his Rome residence, said a break-in at her house could be connected to threats she made to go public.
The women and 17 others have reportedly been questioned by Bari prosecutors who suspect businessman Gianpaolo Tarantini of "abetting prostitution" by paying women to attend parties, including those held by Mr Berlusconi.
Barbara Montereale's car was doused with petrol and set alight after she alleged Mr Tarantini had paid her 1000 euros ($A1747) to attend a party at Mr Berlusconi's holiday home in Sardinia.
Ms Montereale also claimed Ms D'Addario had told her she had sex with Mr Berlusconi in November, after a dinner at his Rome residence.
Ms D'Addario declined to confirm that in an interview with La Repubblica, but did say that Mr Berlusconi had "openly caressed" her on a sofa in front of a bodyguard.
