Three Italian bank bosses involved in a controversial takeover deal this summer have reportedly been arrested.
Mr Fiorani was forced to step down from Banca Popolare Italiana
Gianpiero Fiorani, ex-Banca Popolare Italiana (BPI) boss, was charged with criminal association in market rigging, AP quoted prosecutors as saying.
Also reportedly detained were former chief finance officer Gianfranco Boni and consultant Silvano Spinelli.
Prosecutors are investigating alleged malpractice during BPI's aborted takeover over rival Banca Antonveneta.
They are looking into how BPI and key allies built up large shareholdings in Antonveneta at the height of the bid battle.
Prosecutors are also looking into the role played by Antonio Fazio, governor of the Bank of Italy, in approving the BPI bid.
Critics have accused Mr Fazio of unduly favouring BPI's bid ahead of a rival offer from Dutch bank ANB Amro.
Mr Fazio has denied any wrongdoing and has not been charged with anything.
However, on Tuesday, the European Commission began legal action against the Bank of Italy over its handling of the takeover.
BPI's bid for Antonveneta was frozen by regulators after allegations of impropriety emerged while Mr Fiorani was forced to stand down pending the outcome of the judicial inquiry.
Mr Fiorani's lawyers have yet to make any comment.