No, you still don't understand the law. You can't have a 48h
fermo, just like that. When there is a fermo, a magistrate must be immediately called. Not after 48h. The law says "with no delay". The 48h is a maximum limit, not an option.
There is no charge - and there can't be a police bail - police simply doesn't have that powers, a magistrate won't issue a charge but a charge in any event has nothing to do with arrest; what you need is an issue of cautionary custody, which is simply not going to be agreed to by any judge on a possible charge of theft. Really, you have no chance. You don't have a clue of how things work. It's very funny this strange resisting to believe this legal truth, which is just obvious to any Italian.
Look, you may read a story from a local newspaper, about a man who was caught in flagrante while stealing a bicicle - helping himself with a large iron cutter - he was soptted by an assessor of the city government who called the police. Because called in flagrante, the public minister validated the police arrest. After a few hours he was free again. The following day he was caught again on stealing furhter
two bicicles. Was he arrested? No. This time, not even for an hour. The police didn't see him in the exact moment while he was stealing them, so they only filed the minutes for possesssion of stolen items. He walked free, to stal other bicicles. The police called the immigrant office, who are those who can actually will handle the problem: they will expel him as an illegal immigrant, given that he is from Morocco. The forced expulsion is the "only legal procedure" capable of preventing him from stealing an indefinite number of bicicles.
http://lanuovaferrara.gelocal.it/cronaca/2013/06/25/news/il-bis-del-ladro-di-biciclette-appena-libero-ruba-ancora-1.7318425