Berlusconi, his lawyers and several young women including the ex-prostitute nicknamed "Ruby the Heart Stealer", are being investigated in the wake of the July verdict, which the media magnate has appealed.
The billionaire has denied having sex with Ruby at what prosecutors had described as erotic parties held at his luxury residence outside Milan.
The scandal-tainted 77-year-old is now being investigated for having corrupted witnesses, including by paying the women at the parties monthly sums to testify that the gatherings were just innocent dinners.
The three-time premier -- no stranger to the courts during his political career -- was also sentenced to a year in prison for tax fraud last year which led to his ouster from parliament and stripped of his protection from the law.